Communication system, transmitter, receiver, communication method, program, and communication cable

ABSTRACT

The present invention relates to a communication system, a transmitter, a receiver, a communication method, a program, and a communication cable for providing high-speed bidirectional communication while maintaining compatibility. When an HDMI (R) source performs bidirectional IP communication with an HDMI (R) sink using a CEC line and a signal line, a switching control unit controls a switch so that, when data is transmitted, the switch selects a constituent signal forming a differential signal output from a converting unit and, when data is transmitted, the switch selects a constituent signal forming a differential signal output from a receiver. When bidirectional communication is performed using only the CEC line, the switching control unit controls the switch so that the CEC signal output from the HDMI (R) source or the receiver is selected. The present invention is applicable to, for example, HDMI (R).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/324,732 filed on Jul. 7, 2014, which is a continuation of U.S. patentapplication Ser. No. 13/546,133, (U.S. Pat. No. 8,860,887) filed on Jul.11, 2012, which is a divisional of U.S. patent application Ser. No.12/794,115, (U.S. Pat. No. 8,243,204) filed on Jun. 4, 2010, which is acontinuation of U.S. application Ser. No. 12/312,428, (U.S. Pat. No.7,936,401) filed on Dec. 31, 2009, which is a national phase entry under35 U.S.C. §371 of International Application No. PCT/JP2007/071600 filedNov. 7, 2007, published on May 15, 2008 as WO 2008/056686 A1, whichclaims priority from Japanese Patent Application No. JP 2006-301486,filed in the Japanese Patent Office on Nov. 7, 2006 and from JapanesePatent Application No. JP 2007-050426, filed in the Japanese PatentOffice on Feb. 28, 2007, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a communication system, a transmitter,a receiver, a communication method, a program, and a communication cableand, in particular, to a communication system, a transmitter, areceiver, a communication method, a program, and a communication cablethat provide high speed communication and that have compatibility with acommunication interface capable of unidirectional high-speedtransmission of pixel data of uncompressed images, such as HighDefinition Multimedia Interface (HDMI) (R).

BACKGROUND ART

In recent years, HDMI (R) has been in widespread use as a high-speedcommunication interface for transmitting at high speed a digitaltelevision signal, i.e., pixel data of uncompressed (baseband) imagesand audio data associated with the images, for example, from a digitalversatile disc (DVD) recorder, a set-top box, or other audio visual (AV)sources to a television set, a projector, or other displays.

The HDMI specification defines Transition Minimized DifferentialSignaling (TMDS) channel for high speed unidirectional transmission ofpixel data and audio data from an HDMI (R) source to an HDMI (R) sinkand Consumer Electronics Control line (CEC line) for bidirectionalcommunication between an HDMI (R) source and an HDMI (R) sink, and thelike.

For example, as shown in FIG. 1, pixel data and audio data can betransmitted at high speed by connecting a digital television set 11 toan AV amplifier 12 using an HDMI (R) cable 13 that complies with theHDMI (R) specification.

The digital television set 11 and AV amplifier 12 and a reproducingapparatus 14 are placed in a living room of a user house. In FIG. 1, theliving room is located on the left side. The digital television set 11is connected to the AV amplifier 12 using the HDMI (R) cable 13. The AVamplifier 12 is connected to the reproducing apparatus 14 using an HDMI(R) cable 15.

In addition, a hub 16 is placed in the living room. The digitaltelevision set 11 and reproducing apparatus 14 are connected to the hub16 using local area network (LAN) cables 17 and 18, respectively. In abedroom located to the right of the living room in the drawing, adigital television set 19 is placed. The digital television set 19 isconnected to the hub 16 via a LAN cable 20.

For example, when content recorded in the reproducing apparatus 14 isplayed back and an image is displaying on the digital television set 11,the reproducing apparatus 14 decodes pixel data and audio data servingas the playback content. Thereafter, the reproducing apparatus 14supplies the decoded uncompressed pixel data and audio data to thedigital television set 11 via the HDMI (R) cable 15, the AV amplifier12, and the HDMI (R) cable 13. On the basis of the pixel data and audiodata supplied from the reproducing apparatus 14, the digital televisionset 11 displays images and outputs sounds.

When content recorded in the reproducing apparatus 14 is played back andimages are displayed on the digital television sets 11 and 19 at thesame time, the reproducing apparatus 14 supplies compressed pixel dataand audio data serving as the content to be played back to the digitaltelevision set 11 via the LAN cable 18, the hub 16, and the LAN cable17. In addition, the reproducing apparatus 14 supplies the compressedpixel data and audio data to the digital television set 19 via the LANcable 18, the hub 16, and the LAN cable 20.

The digital television sets 11 and 19 decode the pixel data and audiodata supplied from the reproducing apparatus 14, display images, andoutput sounds on the basis of the decoded uncompressed pixel data andaudio data.

When the digital television set 11 receives pixel data and audio datafor playing back a program over television broadcasting and it thereceived audio data is audio data of, for example, 5.1-channel surroundsounds which the digital television set 11 is unable to decode, thedigital television set 11 converts the audio data into an optical signaland transmits the optical signal to the AV amplifier 12.

Upon receiving the optical signal transmitted from the digitaltelevision set 11, the AV amplifier 12 photoelectrically converts theoptical signal into audio data. Thereafter, the AV amplifier 12 decodesthe converted audio data. Subsequently, the AV amplifier 12 amplifiesthe decoded uncompressed audio data when necessary so as to outputsounds from surround speakers connected thereto. In this manner, thedigital television set 11 can play back a 5.1-channel surroundtelevision program by decoding the received pixel data and displayingimages by using the decoded pixel data and by outputting sounds from theAV amplifier 12 in accordance with the audio data supplied to the AVamplifier 12.

In addition, an HDMI (R)-based apparatus has been proposed in which,when pixel data and audio data are transmitted from an HDMI (R) sourceto an HDMI (R) sink, unnecessary data is muted by turning on/off thedata transmission (refer to, for example, Patent Document 1).

Furthermore, an HDMI (R)-based apparatus has been proposed in which, byusing a selector switch and selecting a terminal from which the pixeldata and audio data are output, an HDMI (R) source can output pixel dataand audio data to a desired HDMI (R) sink among a plurality of HDMI (R)sinks without changing cable connection between the HDMI (R) source andthe HDMI (R) sink (refer to, for example, Patent Document 2).

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2005-57714

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2006-19948

DISCLOSURE OF INVENTION Technical Problem

As noted above, using HDMI (R), pixel data and audio data can betransmitted unidirectionally at high speed from an HDMI (R) source to anHDMI (R) sink. In addition, bidirectional communication can be performedbetween an HDMI (R) source and an HDMI (R) sink.

However, a transmission rate of bidirectional communication allowed bycurrent HDMI (R) is about several hundred bps. Therefore, high-speedbidirectional communication, such as bidirectional Internet protocol(IP) communication, cannot be performed between an HDMI (R) source andan HDMI (R) sink.

Accordingly, when apparatuses including the apparatus described inPatent Documents 1 and 2 perform bidirectional IP communication usingHDMI (R), an amount of data transmitted over IP communication islimited. If a large amount of data is transmitted over IP communication,long delay times occur with communication. It is therefore difficult touse HDMI (R), for example, in an application requiring bidirectionaltransmission of a large amount of data, such as compressed images, or inan application requiring a high speed response.

Accordingly, for example, pins dedicated to high-speed bidirectional IPcommunication may be provided to connectors of an HDMI (R) source and anHDMI (R) sink, and high-speed bidirectional IP communication may beperformed using the dedicated pins.

However, if the dedicated pins are provided to current HDMI (R)-basedconnectors, compatibility with existing HDMI (R) cannot be maintained.

Accordingly, the present invention provides a high-speed bidirectionalcommunication interface having compatibility with a communicationinterface capable of unidirectionally transmitting pixel data ofuncompressed images at high speed (e.g., HDMI (R)).

Technical Solution

According to a first aspect of the present invention, a communicationsystem includes a transmitter for unidirectionally transmitting, to areceiver using a first differential signal, pixel data of anuncompressed image of one screen during an effective video periodrepresenting a period from one vertical synchronization signal to thenext vertical synchronization signal excluding horizontal blankingintervals and a vertical blanking interval, and the receiver forreceiving the first differential signal transmitted from thetransmitter. The transmitter includes first converting means forconverting transmission data different from the pixel data into a seconddifferential signal formed from a first constituent signal and a secondconstituent signal, transmitting the first constituent signal to thereceiver via a first signal line, and outputting the second constituentsignal, first selecting means for selecting one of a transmission signalrelated to a control operation and the second constituent signal outputfrom the first converting means and transmitting the selected signal tothe receiver via a second signal line, first control means forperforming control so that, when the transmission signal is transmittedto the receiver, the transmission signal is selected by the firstselecting means and, when the second differential signal is transmittedto the receiver, the second constituent signal is selected by the firstselecting means, and first decoding means for receiving a thirddifferential signal transmitted from the receiver and decoding the thirddifferential signal into original data. The receiver includes secondconverting means for converting transmission data different from thepixel data into the third differential signal and transmitting the thirddifferential signal to the transmitter, second decoding means forreceiving the second differential signal transmitted from thetransmitter and decoding the second differential signal into originaldata, second selecting means for selecting one of the transmissionsignal and the second constituent signal, and second control means forperforming control so that, when the transmission signal is received,the transmission signal is selected and received by the second selectingmeans and, when the second differential signal is received, the secondconstituent signal is selected by the second selecting means and thesecond constituent signal is received by the second decoding means.

According to the first aspect of the present invention, a communicationmethod for use in a communication system including a transmitter and areceiver is provided. The transmitter unidirectionally transmits, to thereceiver using a first differential signal, pixel data of anuncompressed image of one screen during an effective video periodrepresenting a period from one vertical synchronization signal to thenext vertical synchronization signal excluding horizontal blankingintervals and a vertical blanking interval, and the receiver receivesthe first differential signal transmitted from the transmitter. Thetransmitter includes first converting means for converting transmissiondata different from the pixel data into a second differential signalformed from a first constituent signal and a second constituent signal,transmitting the first constituent signal to the receiver via a firstsignal line, and outputting the second constituent signal, firstselecting means for selecting one of a transmission signal related to acontrol operation and the second constituent signal output from thefirst converting means and transmitting the selected signal to thereceiver via a second signal line, and first decoding means forreceiving a third differential signal transmitted from the receiver anddecoding the third differential signal into original data. The receiverincludes second converting means for converting transmission datadifferent from the pixel data into the third differential signal andtransmitting the third differential signal to the transmitter, seconddecoding means for receiving the second differential, signal transmittedfrom the transmitter and decoding the second differential signal intooriginal data, and second selecting means for selecting one of thetransmission signal and the second constituent signal. The methodincludes the steps of performing control so that, when the transmissionsignal is transmitted to the receiver, the transmission signal isselected by the first selecting means and, when the second differentialsignal is transmitted to the receiver, the second constituent signal isselected by the first selecting means, and performing control so that,when the transmission signal is received by the receiver, thetransmission signal is selected and received by the second selectingmeans and, when the second differential signal is received by thereceiver, the second constituent signal is selected by the secondselecting means and the second constituent signal is received by thesecond decoding means.

According to the first aspect of the present invention, in thetransmitter, the transmission data different from the pixel data isconverted into the second differential signal formed from the firstconstituent signal and second constituent signal, the first constituentsignal is transmitted to the receiver via the first signal line, thesecond constituent signal is output, one of the transmission signalrelated to a control operation and the output second constituent signalis selected, and the selected signal is transmitted to the receiver viathe second signal line. Here, control is performed so that, when thetransmission signal is transmitted to the receiver, the transmissionsignal is selected and, when the second differential signal istransmitted to the receiver, the second constituent signal is selected.In addition, the third differential signal transmitted from the receiveris received and decoded into the original data.

In contrast, in the receiver, the transmission data different from thepixel data is converted into the third differential signal, and thethird differential signal is transmitted to the transmitter, the seconddifferential signal transmitted from the transmitter is received anddecoded into the original data, and one of the transmission signal andthe second constituent signal is selected. Here, control is performed sothat, when the transmission signal is received, the transmission signalis selected and received and, when the second differential signal isreceived, the second constituent signal is selected and received.

According to a second aspect of the present invention, a transmitter isprovided. The transmitter unidirectionally transmits, to a receiverusing a first differential signal, pixel data of an uncompressed imageof one screen during an effective video period representing a periodfrom one vertical synchronization signal to the next verticalsynchronization signal excluding horizontal blanking intervals and avertical blanking interval. The transmitter includes converting meansfor converting transmission data different from the pixel data into asecond differential signal formed from a first constituent signal and asecond constituent signal, transmitting the first constituent signal tothe receiver via a first signal line, and outputting the secondconstituent signal, first selecting means for selecting one of a firsttransmission signal related to a control operation and the secondconstituent signal output from the first converting means andtransmitting the selected signal to the receiver via a second signalline, first control means for performing control so that, when the firsttransmission signal is transmitted to the receiver, the firsttransmission signal is selected by the first selecting means and, whenthe second differential signal is transmitted to the receiver, thesecond constituent signal is selected by the first selecting means, anddecoding means for receiving a third differential signal formed from athird constituent signal and a fourth constituent signal transmittedfrom the receiver and decoding the third differential signal intooriginal data.

The decoding means can receive the third differential signal formed fromthe third constituent signal transmitted via the second signal line andthe fourth constituent signal transmitted via the first signal line, thefirst selecting means can select one of the second constituent signaland the third constituent signal, or the first transmission signal and,when the third differential signal is received, the first control meanscan perform control so that the third constituent signal is selected bythe first selecting means, and the third constituent signal is receivedby the decoding means.

The first selecting means can select one of the second constituentsignal and the third constituent signal or one of the first transmissionsignal and a reception signal related to a control operation transmittedfrom the receiver via the second signal line. When the reception signalis selected, the first selecting means can receive and output theselected reception signal.

The decoding means can receive the third differential signal formed fromthe third constituent signal transmitted via a third signal line and thefourth constituent signal transmitted via a fourth signal line, and thetransmitter can further include second selecting means for selecting oneof the third constituent signal and a second transmission signal relatedto a control operation to be transmitted to the receiver, thirdselecting means for selecting one of the fourth constituent signal and athird transmission signal to be transmitted to the receiver, and secondcontrol means for performing control so that, when the secondtransmission signal and the third transmission signal are transmitted tothe receiver, the second selecting means selects the second transmissionsignal and the second transmission signal is transmitted to the receivervia the third signal line, and the third selecting means selects thethird transmission signal and the third transmission signal istransmitted to the receiver via the fourth signal line and, when thethird differential signal is received, the second selecting meansselects the third constituent signal so that the third constituentsignal is received by the decoding means and the third selecting meansselects the fourth constituent signal so that the fourth constituentsignal is received by the decoding means.

The first selecting means can select one of the second constituentsignal and one of the first transmission signal and a first receptionsignal related to a control operation and transmitted from the receivervia the second signal line. When the first reception signal is selected,the selected first reception signal can be received and output, and thesecond selecting means can select one of the third constituent signaland one of the second transmission signal and a second reception signalrelated to a control operation and transmitted from the receiver via thethird signal line. When the second reception signal is selected, theselected second reception signal can be received and output.

The first transmission signal and the first reception signal can be CEC(Consumer Electronics Control) signals serving as control data for thetransmitter or the receiver. The second reception signal can be E-EDID(Enhanced Extended Display Identification Data) serving as informationregarding a performance of the receiver and used for a controloperation, and data to be converted into the second differential signaland data obtained by decoding the third differential signal can be datathat comply with Internet protocol (IP). The first control means cancontrol the first selecting means so that the second constituent signalis selected after the second reception signal is received, and thesecond control means can control the second selecting means and thethird selecting means so that the third constituent signal and thefourth constituent signal are selected after the second reception signalis received.

According to the second aspect of the present invention, a communicationmethod for use in a transmitter or a program executed by a computer thatcontrols the transmitter is provided. The transmitter unidirectionallytransmits, to a receiver using a first differential signal, pixel dataof an uncompressed image of one screen during an effective video periodrepresenting a period from one vertical synchronization signal to thenext vertical synchronization signal excluding horizontal blankingintervals and a vertical blanking interval. The transmitter includesfirst converting means for converting transmission data different fromthe pixel data into a second differential signal formed from a firstconstituent signal and a second constituent signal, transmitting thefirst constituent signal to the receiver via a first signal line, andoutputting the second constituent signal, selecting means for selectingone of a transmission signal related to a control operation and thesecond constituent signal output from the first converting means andtransmitting the selected signal to the receiver via a second signalline, and decoding means for receiving a third differential signaltransmitted from the receiver and decoding the third differential signalinto original data. The method or program includes the step ofperforming control so that, when the transmission signal is transmittedto the receiver, the transmission signal is selected by the selectingmeans and, when the second differential signal is transmitted to thereceiver, the second constituent signal is selected by the selectingmeans.

According to the second aspect of the present invention, thetransmission data different from the pixel data is converted into thesecond differential signal formed from the first constituent signal andthe second constituent signal, the first constituent signal istransmitted to the receiver via the first signal line, the secondconstituent signal is output. One of a first transmission signal relatedto a control operation and the output second constituent signal isselected, and the selected signal is transmitted to the receiver via thesecond signal line. Here, control is performed so that, when the firsttransmission signal is transmitted to the receiver, the firsttransmission signal is selected and, when the second differential signalis transmitted to the receiver, the second constituent signal isselected. In addition, the third differential signal formed from a thirdconstituent signal and a fourth constituent signal transmitted from thereceiver is received and decoded into the original data.

According to a third aspect of the present invention, a receiver isprovided. The receiver receives, using a first differential signal,pixel data of an uncompressed image of one screen unidirectionallytransmitted from a transmitter during an effective video periodrepresenting a period from one vertical synchronization signal to thenext vertical synchronization signal excluding horizontal blankingintervals and a vertical blanking interval. The receiver includesdecoding means for receiving a second differential signal formed from afirst constituent signal transmitted from the transmitter via a firstsignal line and a second constituent signal transmitted from thetransmitter via a second signal line and decoding the seconddifferential signal to original data, first selecting means forselecting one of the first constituent signal and a first receptionsignal related to a control operation and transmitted from thetransmitter via the first signal line, first control means forperforming control so that, when the first reception signal is received,the first reception signal is selected and received by the firstselecting means and, when the second differential signal is received,the first constituent signal is selected by the first selecting meansand is received by the decoding means, and converting means forconverting transmission data different from the pixel data into a thirddifferential signal formed from a third constituent signal and a fourthconstituent signal and transmitting the third differential signal to thetransmitter.

The converting means can output the third constituent signal andtransmit the fourth constituent signal to the transmitter via the secondsignal line. The first selecting means can select one of the firstreception signal and one of the first constituent signal and the thirdconstituent signal output from the converting means, and the firstcontrol means can perform control so that, when the third differentialsignal is transmitted, the first selecting means selects the thirdconstituent signal, and the third constituent signal is transmitted tothe transmitter via the first signal line.

The first selecting means can select one of the first constituent signaland the third constituent signal or one of the first reception signaland a transmission signal related to a control operation. When thetransmission signal is selected, the selected transmission signal can betransmitted to the transmitter via the first signal line.

The converting means can output the third constituent signal and thefourth constituent signal, and the receiver can further include secondselecting means for selecting one of the third constituent signal outputfrom the converting means and a second reception signal related to acontrol operation and transmitted from the transmitter via a thirdsignal line, third selecting means for selecting one of the fourthconstituent signal output from the converting means and a thirdreception signal transmitted from the transmitter via a fourth signalline, and second control means for performing control so that, when thesecond reception signal and the third reception signal are received, thesecond reception signal is selected and received by the second selectingmeans, and the third reception signal is selected and received by thethird selecting means and, when the third differential signal istransmitted, the third constituent signal is selected by the secondselecting means and is transmitted to the transmitter via the thirdsignal line, and the fourth constituent signal is selected by the thirdselecting means and is transmitted to the transmitter via the fourthsignal line.

The first selecting means can select one of the first constituent signaland one of the first reception signal and a first transmission signalrelated to a control operation and to be transmitted to the transmitter.When the first transmission signal, is selected, the selected firsttransmission signal can be transmitted to the transmitter via the firstsignal line, and the second selecting means can select one of the thirdconstituent signal and one of the second reception signal and a secondtransmission signal related to a control operation and to be transmittedto the transmitter. When the second transmission signal is selected, theselected second transmission signal can be transmitted to thetransmitter via the third signal line.

According to the third aspect of the present invention, a communicationmethod for use in a receiver or a program executed by a computer thatcontrols the receiver is provided. The receiver receives, using a firstdifferential signal, pixel data of an uncompressed image of one screenunidirectionally transmitted from a transmitter during an effectivevideo period representing a period from one vertical synchronizationsignal to the next vertical synchronization signal excluding horizontalblanking intervals and a vertical blanking interval. The receiverincludes decoding means for receiving a second differential signalformed from a first constituent signal transmitted from the transmittervia a first signal line and a second constituent signal transmitted fromthe transmitter via a second signal line and decoding the seconddifferential signal to original data, selecting means for selecting oneof the first constituent signal and a reception signal related to acontrol operation and transmitted from the transmitter via the firstsignal line, and converting means for converting transmission datadifferent from the pixel data into a third differential signal andtransmitting the third differential signal to the transmitter. Themethod or the program includes the step of performing control so that,when the reception signal is received, the reception signal is selectedby the selecting means and is received and, when the second differentialsignal is received, the first constituent signal is selected by theselecting means and is received by the decoding means.

According to the third aspect of the present invention, the seconddifferential signal formed from the first constituent signal transmittedfrom the transmitter via the first signal line and the secondconstituent signal transmitted from the transmitter via the secondsignal line is received and decoded into the original data. One of thefirst constituent signal and the first reception signal related to acontrol operation and transmitted from the transmitter via the firstsignal line is selected. Here, control is performed so that, when thefirst reception signal is received, the first reception signal isselected and received and, when the second differential signal isreceived, the first constituent signal is selected and received. Inaddition, the transmission data different from the pixel data isconverted into a third differential signal formed from a thirdconstituent signal and a fourth constituent signal, and the thirddifferential signal is transmitted to the transmitter.

According to a fourth aspect of the present invention, a communicationcable for connecting between a transmitter and a receiver is provided.The transmitter unidirectionally transmits, using a first differentialsignal, pixel data of an uncompressed image of one screen to thereceiver during an effective video period representing a period from onevertical synchronization signal to the next vertical synchronizationsignal excluding horizontal blanking intervals and a vertical blankinginterval. The transmitter includes first converting means for convertingtransmission data different from the pixel data into a seconddifferential signal formed from a first constituent signal and a secondconstituent signal, transmitting the first constituent signal to thereceiver via a first signal line, and outputting the second constituentsignal, first selecting means for selecting one of a transmission signalrelated to a control operation and the second constituent signal outputfrom the first converting means and transmitting the selected signal tothe receiver via a second signal line, first control means forperforming control so that, when the transmission signal is transmittedto the receiver, the transmission signal is selected by the firstselecting means and, when the second differential signal is transmittedto the receiver, the second constituent signal is selected by the firstselecting means, and first decoding means for receiving a thirddifferential signal transmitted from the receiver and decoding the thirddifferential signal into original data. The receiver receives the firstdifferential signal transmitted from the transmitter. The receiverincludes second converting means for converting transmission datadifferent from the pixel data into the third differential signal andtransmitting the third differential signal to the transmitter, seconddecoding means for receiving the second differential signal transmittedfrom the transmitter and decoding the second differential signal tooriginal data, second selecting means for selecting one of the secondconstituent signal and the transmission signal, and second control meansfor performing control so that, when the transmission signal isreceived, the transmission signal is selected by the second selectingmeans and is received and, when the second differential signal isreceived, the second constituent signal is selected by the secondselecting means and is received by the second decoding means. Thecommunication cable includes the first signal line and the second signalline. The first signal line and the second signal line are twistedtogether so as to form a twisted wire differential pair.

According to the fourth aspect of the present invention, thecommunication cable for connecting between the transmitter and thereceiver includes a first signal line and a second signal line. Thefirst signal line and the second signal line are twisted together so asto form a twisted wire differential pair.

According to a fifth aspect of the present invention, a communicationsystem including an interface for performing transmission of video dataand audio data, exchange and authentication of connected deviceinformation, communication of device control data, and LAN communicationby using a single cable, the communication system is provided. Thecommunication system includes a pair of differential transmission linesthat allow a connectable device to be connected thereto. The LANcommunication is performed through bidirectional communication via thepair of differential transmission lines, and the communication systemhas a function of notifying a connection state of the interface by usinga DC bias potential of at least one of the differential transmissionlines of the pair.

According to a sixth aspect of the present invention, a communicationsystem including an interface for performing transmission of video dataand audio data, exchange and authentication of connected deviceinformation, communication of device control data, and LANcommunication, by using a single cable is provided. The communicationsystem includes two pairs of differential transmission lines that allowa connectable device to be connected thereto. The LAN communication isperformed through unidirectional communication via the two pairs ofdifferential transmission lines. The communication system has a functionof notifying a connection state of the interface by using a DC biaspotential of at least one of the differential transmission lines, and atleast two transmission lines are used for exchange and authentication ofconnected device information in a time multiplexing manner with the LANcommunication.

Advantageous Effects

According to the present invention, bidirectional communication can beperformed. In particular, high-speed bidirectional communication can beperformed in, for example, a communication interface that canunidirectionally transmit pixel data of an uncompressed image and audiodata associated with the image at high speed while maintainingcompatibility.

In addition, according to the present invention, a circuit used for LANcommunication can be formed regardless of the electrical specificationdefined for the DDC. As a result, stable and reliable LAN communicationcan be realized at low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a widely usedimage transmission system.

FIG. 2 is a diagram illustrating the configuration of an imagetransmission system according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of the structure of an HDMI(R) source and an HDMI (R) sink.

FIG. 4 is a diagram illustrating the pin assignment of a connector ofType-A of HDMI (R).

FIG. 5 is a diagram illustrating the pin assignment of a connector ofType-C of HDMI (R).

FIG. 6 is a diagram illustrating an example of the configuration of theHDMI (R) source and the HDMI (R) sink in more detail.

FIG. 7 is a diagram illustrating another example of the configuration ofthe HDMI (R) source and the HDMI (R) sink in more detail.

FIG. 8 is a diagram illustrating the data structure of E-EDID.

FIG. 9 is a diagram illustrating the data structure of Vender Specific.

FIG. 10 is a flowchart illustrating a communication process performed bythe HDMI (R) source.

FIG. 11 is a flowchart illustrating a communication process performed bythe HDMI (R) sink.

FIG. 12 is a flowchart illustrating a communication process performed bythe HDMI (R) source.

FIG. 13 is a flowchart illustrating a communication process performed bythe HDMI (R) sink.

FIG. 14 is a diagram illustrating another example of the configurationof the HDMI (R) source and the HDMI (R) sink in more detail.

FIG. 15 is a flowchart illustrating a communication process performed bythe HDMI (R) source.

FIG. 16 is a flowchart illustrating a communication process performed bythe HDMI (R) sink.

FIG. 17 is a block diagram illustrating an example of the configurationof a computer according to an embodiment of the present invention.

FIG. 18 is a circuit diagram illustrating a first example of theconfiguration of a communication system in which the connection state ofan interface is notified by using a DC bias potential of at least one oftwo transmission lines.

FIG. 19 is a diagram illustrating an example of the configuration of asystem when the system is connected to Ethernet (registered trademark).

FIG. 20 is a circuit diagram illustrating a second example of theconfiguration of the communication system in which the connection stateof an interface is notified by using a DC bias potential of at least oneof two transmission lines.

FIG. 21 is a diagram illustrating bidirectional communication waveformsin the communication system having the configuration examples.

EXPLANATION OF REFERENCE NUMERALS

35 HDMI (R) cable, 71 HDMI (R) source, 72 HDMI (R) sink, 81 transmitter,82 receiver, 83 DDC, 84 CEC line, 85 EDIDROM, 121 switching controlunit, 124 switching control unit, 131 converting unit, 132 decodingunit, 133 switch, 134 converting unit, 135 switch, 136 decoding unit,141 signal line, 171 switching control unit, 172 switching control unit,181 switch, 182 switch, 183 decoding unit, 184 converting unit, 185switch, 186 switch, 191 SDA line, 192 SCL line, 400 communicationsystem, 401 LAN function expansion HDMI (EH) source device, 411 LANsignal transmitter circuit, 412 terminating resistor, 413, 414 ACcoupling capacitor, 415 LAN signal receiver circuit, 416 subtractingcircuit, 421 pull-up resistor, 422 resistor, 423 capacitor, 424comparator, 431 pull-down resistor, 432 resistor, 433 capacitor, 434comparator, 402 EH sink device, 441 LAN signal transmitter circuit, 442terminating resistor, 443, 444 AC coupling capacitor, 445 LAN signalreceiver circuit, 446 subtracting circuit, 451 pull-down resistor, 452resistor, 453 capacitor, 454 comparator, 461 choke coil, 462, 463resistor, 403 EH cable, 501 Reserved line, 502 HPD Line, 511, 512 sourceside terminal, 521, 522 sink side terminal, 600 communication system,601 LAN function expansion HDMI (EH) source device, 611 LAN signaltransmitter circuit, 612, 613 terminating resistor, 614-617 AC couplingcapacitor, 618 LAN signal receiver circuit, 620 inverter, 621 resistor,622 resistor, 623 capacitor, 624 comparator, 631 pull-down resistor, 632resistor, 633 capacitor, 634 comparator, 640 NOR gate, 641-644 analogswitch, 645 inverter, 646, 647 analog switch, 651, 652 DDC transceiver,653, 654 pull-up resistor, 602 EH sink device, 661 LAN signaltransmitter circuit, 662, 663 terminating resistor, 664-667 AC couplingcapacitor, 668 LAN signal receiver circuit, 671 pull-down resistor, 672resistor, 673 capacitor, 674 comparator, 681 choke coil, 682, 683resistor, 691-694 analog switch, 695 inverter, 696, 697 analog switch,701, 702 DDC transceiver, 703 pull-up resistor, 603 EH cable, 801Reserved line, 802 HPD line, 803 SCL line, 804 SDA line, 811-814 sourceside terminal, 821-824 sink side terminal

BEST MODES FOR CARRYING OUT THE INVENTION

Exemplary embodiments of the present invention are described below withreference to the accompanying drawings.

FIG. 2 illustrates the configuration of an image transmission systemaccording to an embodiment of the present invention.

The image transmission system includes a digital television set 31, anamplifier 32, a reproducing apparatus 33 and a digital television set34. The digital television set 31 is connected to the amplifier 32 usingan HDMI (R) cable 35 that complies with HDMI (R) requirements, and theamplifier 32 is connected to the reproducing apparatus 33 using an HDMI(R) cable 36 that complies with HDMI (R) requirements. In addition, thedigital television set 31 is connected to the digital television set 34using a LAN cable 37 for a LAN, such as the Ethernet (registeredtrademark).

In the example shown in FIG. 2, the digital television set 31, theamplifier 32, and the reproducing apparatus 33 are placed in a livingroom located on the left of FIG. 2, and the digital television set 34 isinstalled in a bedroom located to the right of the living room.

The reproducing apparatus 33 is, for example, a DVD player, a hard discrecorder or the like. The reproducing apparatus 33 decodes pixel dataand audio data used for reproducing content, and supplies the resultantuncompressed pixel data and audio data to the amplifier 32 via the HDMI(R) cable 36.

The amplifier 32 may be composed of an AV amplifier. The amplifier 32receives pixel data and audio data from the reproducing apparatus 313and amplifies the supplied audio data as needed. In addition, theamplifier 32 supplies the audio data supplied from the reproducingapparatus 33 and amplified as needed and the pixel data supplied fromthe reproducing apparatus 33 to the digital television set 31 via theHDMI (R) cable 35. On the basis of the pixel data and audio datasupplied from the amplifier 32, the digital television set 31 displaysimages and outputs sound so as to play back the content.

In addition, the digital television set 31 and the amplifier 32 canperform high-speed bidirectional communication, such as IPcommunication, by using the HDMI (R) cable 35, and the amplifier 32 andthe reproducing apparatus 33 can also perform high-speed bidirectionalcommunication, such as IP communication, by using the HDMI (R) cable 36.

That is, for example, the reproducing apparatus 33 can transmit, to theamplifier 32, compressed pixel data and audio data as data that complieswith IP standards via the HDMI (R) cable 36 by performing IPcommunication with the amplifier 32. The amplifier 32 can receive thecompressed pixel data and audio data transmitted from the reproducingapparatus 33.

In addition, by performing IP communication with the digital televisionset 31, the amplifier 32 can transmit, to the digital television set 31,compressed pixel data and audio data as data that complies with IP viathe HDMI (R) cable 35. The digital television set 31 can receive thecompressed pixel data and audio data transmitted from the amplifier 32.

Thus, the digital television set 31 can transmit the received pixel dataand audio data to the digital television set 34 via the LAN cable 37. Inaddition, the digital television set 31 decodes the received pixel dataand audio data. Thereafter, on the basis of the resultant uncompressedpixel data and audio data, the digital television set 31 displays imagesand outputs sound so as to play back the content.

The digital television set 34 receives and decodes the pixel data andaudio data transmitted from the digital television set 31 via the LANcable 37. Thereafter, on the basis of the uncompressed pixel data andaudio data obtained through the decoding, the digital television set 34displays images and outputs sound so as to play back the content. Inthis manner, the digital television sets 31 and 34 can play back thesame or different content items at the same time.

Furthermore, when the digital television set 31 receives pixel data andaudio data for playing back a television broadcasting program serving ascontent and if the received audio data is audio data, such as5.1-channel surround sound, that the digital television set 31 cannotdecode, the digital television set 31 transmits the received audio datato the amplifier 32 via the HDMI (R) cable 35 by performing IPcommunication with the amplifier 32.

The amplifier 32 receives and decodes the audio data transmitted fromthe digital television set 31. Thereafter, the amplifier 32 amplifiesthe decoded audio data as needed so as to play back the 5.1-channelsurround sound using speakers (not shown) connected to the amplifier 32.

The digital television set 31 transmits the audio data to the amplifier32 via the HDMI (H) cable 35. In addition, the digital television set 31decodes the received pixel data and plays back the program on the basisof the pixel data obtained through the decoding.

In this manner, in the image transmission system shown in FIG. 2, theelectronic apparatuses, such as the digital television set 31, amplifier32, and reproducing apparatus 33 connected using the HDMI (R) cables 35and 36 can perform IP communication by using the HDMI (R) cables.Accordingly, a LAN cable corresponding to the LAN cable 17 shown in FIG.1 is not needed.

In addition, by connecting the digital television set 31 to the digitaltelevision set 34 using the LAN cable 37, the digital television set 31can further transmit data received from the reproducing apparatus 33 viathe HDMI (R) cable 36, the amplifier 32, and the HDMI (R) cable 35 tothe digital television set 34 via the LAN cable 37. Therefore, a LANcable and an electronic apparatus respectively corresponding to the LANcable 18 and the hub 16 shown in FIG. 1 are not needed.

As shown in FIG. 1, in existing image transmission systems, cables ofdifferent types are required in accordance with transmission/receptiondata and communication methods. Therefore, wiring of cablesinterconnecting electronic apparatuses is complicated. In contrast, inthe image transmission system shown in FIG. 2, high-speed bidirectionalcommunication, such as IP communication, can be performed betweenelectronic apparatuses connected using the HDMI (R) cable. Accordingly,connection between electronic apparatuses can be simplified. That is,existing complicated wiring of cables for connecting electronicapparatuses can be further simplified.

Next, FIG. 3 illustrates an example of the configuration of an HDMI (R)source and an HDMI (R) sink incorporated in each of the electronicapparatuses connected to one another using an HDMI (R) cable, forexample, the configuration of an HDMI (R) source provided in theamplifier 32 and an HDMI (R) sink provided in the digital television set31 shown in FIG. 2.

An HDMI (R) source 71 is connected to an HDMI (R) sink 72 using thesingle HDMI (R) cable 35. High-speed bidirectional IP communication canbe performed between the HDMI (R) source 71 and the HDMI (R) sink 72 byusing the HDMI (R) cable 35 while maintaining compatibility with currentHDMI (R).

During an effective video period (hereinafter referred to as an “activevideo period” as needed), which is a period from one verticalsynchronization signal to the next vertical synchronization signalexcluding horizontal blanking intervals and a vertical blankinginterval, the HDMI (R) source 71 unidirectionally transmits adifferential signal corresponding to pixel data of an uncompressed imagefor one screen to the HDMI (R) sink 72 via a plurality of channels. Inaddition, during the horizontal blanking interval or vertical blankinginterval, the HDMI (R) source 71 unidirectionally transmits differentialsignals corresponding to at least audio data and control data associatedwith the image, other auxiliary data and the like, to the HDMI (R) sink72 via a plurality of channels.

That is, the HDMI (R) source 71 includes a transmitter 81. Thetransmitter 81 converts, for example, pixel data of an uncompressedimage into a corresponding differential signal. Thereafter, thetransmitter 81 unidirectionally and serially transmits the differentialsignal to the HDMI (R) sink 72 using three TMDS channels #0, #1 and #2of the HDMI (R) cable 35.

In addition, the transmitter 81 converts audio data associated withuncompressed images, necessary control data, other auxiliary data andthe like, into corresponding differential signals and unidirectionallyand serially transmits the converted differential signals to the HDMI(R) sink 72 connected using the HDMI (R) cable 35 via the three TMDSchannels #0, #1 and #2.

Furthermore, the transmitter 81 transmits, via a TMDS clock channel, apixel clock that is synchronized with the pixel data to be transmittedvia the three TMDS channels #0, #1 and #2, to the HDMI (R) sink 72connected thereto using the HDMI (R) cable 35, 10-bit pixel data istransmitted via each TMDS channel #i (i=0, 1, or 2) during one pixelclock.

The HDMI (R) sink 72 receives the differential signal corresponding tothe pixel data unidirectionally transmitted from the HDMI (R) source 71via the plurality of channels during the active video period. Inaddition, the HDMI (R) sink 72 receives the differential signalscorresponding to the audio data and control data unidirectionallytransmitted from the HDMI (R) source 71 via the plurality of channelsduring the horizontal blanking interval or the vertical blankinginterval.

That is, the HDMI (R) sink 72 includes a receiver 82. The receiver 82receives, via the TMDS channels #0, #1 and #2, the differential signalcorresponding to the pixel data and the differential signalscorresponding to the audio data and control data, which areunidirectionally transmitted from the HDMI (R) source 71 connectedthereto using the HDMI (R) cable 35, in synchronization with the pixelclock also transmitted from the HDMI (R) source 71 via the TMDS clockchannel.

In addition to the three TMDS channels #0 to #2 serving as transmissionchannels used for unidirectionally and serially transmitting the pixeldata and audio data from the HDMI (R) source 71 to the HDMI (R) sink 72in synchronization with the pixel clock and the TMDS clock channelserving as a transmission channel used for transmitting the pixel clock,the transmission channels of the HDMI (R) system including the HDMI (R)source 71 and HDMI (R) sink 72 include transmission channels called adisplay data channel (DDC) 83 and a CEC line 84.

The DDC 83 includes two signal lines (not shown) contained in the HDMI(R) cable 35. The DDC 83 is used when the HDMI (R) source 71 readsenhanced extended display identification data (E-EDID) from the HDMI (R)sink 72 connected thereto using the HDMI (R) cable 35.

That is, in addition to the receiver 82, the HDMI (R) sink 72 includesan EDIDROM (EDID ROM (read only memory)) 85 storing the E-EDIDrepresenting information on the settings and performance of the HDMI (R)sink 72. The HDMI (R) source 71 reads, via the DDC 83, the E-EDID storedin the EDIDROM 85 of the HDMI (R) sink 72 connected thereto using theHDMI (R) cable 35. Thereafter, on the basis of the E-EDID, the HDMI (R)source 71 recognizes the settings and performance of the HDMI (R) sink72, i.e., for example, an image format (a profile) supported by the HDMI(R) sink 72 (an electronic apparatus including the HDMI (R) sink 72).Examples of the image format include RGB (red, green, blue), YCbCr4:4:4, and YCbCr 4:2:2.

Although not shown, like the HDMI (R) sink 72, the HDMI (R) source 71can store the E-EDID and transmit the E-EDID to the HDMI (R) sink 72 asneeded.

The CEC line 84 includes one signal line (not shown) contained in theHDMI (R) cable 35. The CEC line 84 is used for bidirectionalcommunication of the control data between the HDMI (R) source 71 andHDMI (R) sink 72.

The HDMI (R) source 71 and HDMI (R) sink 72 can perform bidirectional IPcommunication by transmitting a frame that complies with IEEE (Instituteof Electrical and Electronics Engineers) 802.3 to the HDMI (R) sink 72and HDMI (R) source 71, respectively, via the DDC 83 or the CEC line 84.

In addition, the HDMI (R) cable 35 includes a signal line 86 connectedto a pin called Hot Plug Detect. By using this signal line 86, the HDMI(R) source 71 and the HDMI (R) sink 72 can detect connection of a newelectronic apparatus, that is, the HDMI (R) sink 72 and the HDMI (R)source 71, respectively.

Next, FIGS. 4 and 5 illustrate the pin assignment of a connector (notshown) provided to the HDMI (R) source 71 or the HDMI (R) sink 72. Theconnector is connected to the HDMI (R) cable 35.

Note that, in FIGS. 4 and 5, a pin number for identifying each pin ofthe connector is shown in the left column (the PIN column), and the nameof a signal assigned to the pin identified by the pin number shown inthe left column at the same row is shown in the right column (the SignalAssignment column).

FIG. 4 illustrates the assignment of pins of a connector called Type-Aof HDMI (R).

Two differential signal lines used for transmitting differential signalsTMDS Data#i+ and TMDS Data#i− of a TMDS channel #i are connected to pins(pins having pin numbers 1, 4 and 7) to which TMDS Data#i+ is assignedand pins (pins having pin numbers 3, 6 and 9) to which TMDS Data#i− isassigned.

In addition, the CEC line 84 for transmitting a CEC signal of controldata is connected to a pin having a pin number of 13, and a pin having apin number 14 is a reserved pin. If bidirectional IP communication canbe performed by using this reserved pin, compatibility with current HDMI(R) can be maintained. Accordingly, in order for differential signals tobe transmitted by using the CEC line 84 and a signal line to beconnected to the pin having the pin number 14, the signal line to beconnected to the pin having the pin number 14 and the CEC line 84 aretwisted together so as to form a shielded twisted wire differentialpair. In addition, the signal line and the CEC line 84 are ground to aground line of the CEC line 84 and the DDC 83 connected to a pin havinga pin number 17.

Furthermore, a signal line for transmitting a serial data (SDA) signal,such as the E-EDID, is connected to a pin having a pin number 16, and asignal line for transmitting a serial clock (SCL) signal, which is usedfor transmission/reception synchronization of the SDA signal, isconnected to a pin having a pin number 15. The DDC 83 shown in FIG. 3 iscomposed of the signal line for transmitting the SDA signal and thesignal line for transmitting the SCL signal.

Like the CEC line 84 and the signal line to be connected to the pinhaving the pin number 14, the signal line for transmitting the SDAsignal and the signal line for transmitting the SCL signal are twistedtogether so as to form a shielded twisted wire differential pair andallow differential signals to pass therethrough. The signal line fortransmitting the SDA signal and the signal line for transmitting the SCLsignal are grounded to a ground line that is connected to the pin havingthe pin number 17.

In addition, the signal line 86 for transmitting a signal for detectingconnection of a new electronic apparatus is connected to a pin having apin number 19.

FIG. 5 illustrates the assignment of pins of a connector called Type-Cor a mini-type of HDMI (R).

Two signal lines serving as differential signal lines for transmittingdifferential signals TMDS Data#i+ and TMDS Data#i− of a TMDS channel #iare connected to pins (pins having pin numbers 2, 5 and 8) to which TMDSData#i+ is assigned and pins (pins having pin numbers 3, 6 and 9) towhich TMDS Data#i− is assigned.

In addition, the CEC line 84 for transmitting a CEC signal is connectedto a pin having a pin number of 14, and a pin having a pin number of 17is a reserved pin. As in the case of Type-A, the signal line to beconnected to the pin having the pin number 17 and the CEC line 84 aretwisted together so as to form a shielded twisted wire differentialpair. The signal line and the CEC line 84 are grounded to the groundline of the CEC line 84 and DDC line 83 to be connected to a pin havinga pin number 13.

Furthermore, a signal line for transmitting an SDA signal is connectedto a pin having a pin number 16, while a signal line for transmitting anSCL signal is connected to a pin having a pin number 15. As in the caseof Type-A, the signal line for transmitting the SDA signal and thesignal line for transmitting the SCL signal are twisted together so asto form a shielded twisted wire differential pair and allow differentialsignals to pass therethrough. The signal line for transmitting the SDAsignal and the signal line for transmitting the SCL signal are groundedto a ground line that is connected to the pin having the pin number 13.Still furthermore, the signal line 86 for transmitting a signal fordetecting connection of a new electronic apparatus is connected to a pinhaving a pin number 19.

Next, FIG. 6 is a diagram illustrating the configuration of the HDMI (R)source 71 and HDMI (R) sink 72 for performing IP communication using ahalf duplex communication method via the CEC line 84 and the signal lineconnected to the reserved pin of the HDMI (R) connector. Note that FIG.6 shows an example of the configuration regarding half duplexcommunication between the HDMI (R) source 71 and HDMI (R) sink 72. Inaddition, the same numbering will be used in describing FIG. 6 as wasused in describing FIG. 3, and the description thereof are not repeatedwhere appropriate.

The HDMI (R) source 71 includes the transmitter 81, a switching controlunit 121 and a timing control unit 122. In addition, the transmitter 81includes a converting unit 131, a decoding unit 132, and a switch 133.

The converting unit 131 receives Tx data supplied thereto. The Tx datais data to be transmitted from the HDMI (R) source 71 to the HDMI (R)sink 72 through bidirectional IP communication between the HDMI (R)source 71 and the HDMI (R) sink 72. For example, the Tx data iscompressed pixel data and audio data and the like.

The converting unit 131 includes, for example, a differential amplifier.The converting unit 131 converts the supplied Tx data into adifferential signal having two constituent signals. In addition, theconverting unit 131 transmits the converted differential signal to thereceiver 82 via the CEC line 84 and a signal line 141 connected to areserved pin of a connector (not shown) provided to the transceiver 81.That is, the converting unit 131 supplies one of the constituent signalsforming the converted differential signal to the switch 133 via the CECline 84, more precisely, via the signal line of the transmitter 81connected to the CEC line 84 of the HDMI (R) cable 35. The convertingunit 131 further supplies the other constituent signal of the converteddifferential signal to the receiver 82 via the signal line 141, moreprecisely, via the signal line of the transmitter 81 connected to thesignal line 141 of the HDMI (R) cable 35.

The decoding unit 132 includes, for example, a differential amplifier.Input terminals of the decoding unit 132 are connected to the CEC line84 and the signal line 141. Under the control of the timing control unit122, the decoding unit 132 receives a differential signal transmittedfrom the receiver 82 via the CEC line 84 and the signal line 141, thatis, the differential signal including the constituent signal on the CECline 84 and the constituent signal on the signal line 141. The decodingunit 132 then decodes the differential signal and outputs original Rxdata. As used herein, the term “Rx data” refers to data transmitted fromthe HDMI (R) sink 71 to the HDMI (R) source 71 through bidirectional IPcommunication between the HDMI (R) source 71 and the HDMI (R) sink 72.An example of the Rx data is a command for requesting transmission ofpixel data and audio data, or the like.

At a timing point when data is transmitted, the switch 133 is suppliedwith the CEC signal from the HDMI (R) source 71 or the constituentsignal of the differential signal corresponding to Tx data from theconverting unit 131, while, at a timing point when data is received, theswitch 133 is supplied with the CEC signal from the receiver 82 or theconstituent signal of the differential signal corresponding to Rx datafrom the receiver 82. Under the control of the switching control unit121, the switch 133 selectively outputs the CEC signal from the HDMI (R)source 71, the CEC signal from the receiver 82, the constituent signalof the differential signal corresponding to Tx data, or the constituentsignal of the differential signal corresponding to Rx data.

That is, at a timing point when the HDMI (R) source 71 transmits data tothe HDMI (R) sink 72, the switch 133 selects one of the CEC signalsupplied from HDMI (R) source 71 and the constituent signal suppliedfrom the converting unit 131 and transmits the selected one of the CECsignal and the constituent signal to the receiver 82 via the CEC line84.

In addition, at a timing point when the HDMI (R) source 71 receives datafrom the HDMI (R) sink 72, the switch 133 receives one of the CEC signaltransmitted from the receiver 82 via the CEC line 84 and the constituentsignal of the differential signal corresponding to the Rx data. Theswitch 133 then supplies the received CEC signal or constituent signalto the HDMI (R) source 71 or the decoding unit 132.

The switching control unit 121 controls the switch 133 so that theswitch 133 is switched to select one of the signals supplied to theswitch 133. The timing control unit 122 controls a timing point at whichthe decoding unit 132 receives the differential signal.

In addition, the HDMI (R) sink 72 includes the receiver 82, a timingcontrol unit 223, and a switching control unit 124. Furthermore, thereceiver 82 includes a converting unit 134, a switch 135, and a decodingunit 136.

The converting unit 134 is composed of, for example, a differentialamplifier. The converting unit 134 receives supplied Rx data. Under thecontrol of the timing control unit 123, the converting unit 134 convertsthe supplied Rx data into a differential signal having two constituentsignals and transmits the converted differential signal to thetransmitter 81 via the CEC line 84 and signal line 141. That is, theconverting unit 134 supplies one of the constituent signals forming theconverted differential signal to the switch 135 via the CEC line 84,more precisely, via the signal line provided to the receiver 82connected to the CEC line 84 of the HDMI (R) cable 35, while theconverting unit 134 supplies the other constituent signal forming theconverted differential signal to the transmitter 81 via the signal line141, more precisely, via the signal line provided to the transmitter 81connected to the signal line 141 of the HDMI (R) cable 35.

At a timing point when data is received, the switch 135 is supplied withthe CEC signal from the transmitter 81 or the constituent signal formingthe differential signal corresponding to Tx data from the transmitter81, while, at a timing point when data is transmitted, the switch 135 issupplied with the constituent signal forming the differential signalcorresponding to Rx data from the converting unit 134 or the CEC signalfrom the HDMI (R) sink 72. Under the control of the switching controlunit 124, the switch 135 selectively outputs one of the CEC signal fromthe transmitter 81, the CEC signal from the HDMI (R) sink 72, theconstituent signal forming the differential signal corresponding to Txdata, and the constituent signal forming the differential signalcorresponding to Rx data.

That is, at a timing point when the HDMI (R) sink 72 transmits data tothe HDMI (R) source 71, the switch 135 selects one of the CEC signalsupplied from HDMI (R) sink 72 and the constituent signal supplied fromthe converting unit 134. The switch 135 then transmits the selected CECsignal or constituent signal to the transmitter 81 via the CEC line 84.

In addition, at a timing point when the HDMI (R) sink 72 receives datatransmitted from the HDMI (R) source 71, the switch 135 receives one ofthe CEC signal transmitted from the transmitter 81 via the CEC line 84and the constituent signal of the differential signal corresponding toTx data. The switch 135 then supplies the received CEC signal orconstituent signal to the HDMI (R) sink 72 or the decoding unit 136.

The decoding unit 136 is composed of, for example, a differentialamplifier. Input terminals of the decoding unit 136 are connected to theCEC line 84 and signal line 141. The decoding unit 136 receives adifferential signal transmitted from the transmitter 81 via the CEC line84 and signal line 141, that is, the differential signal formed from theconstituent signal on the CEC line 84 and the constituent signal on thesignal line 141. The decoding unit 136 then decodes the differentialsignal into original Tx data and outputs the original Tx data.

The switching control unit 124 controls the switch 135 so that theswitch 135 is switched to select one of the signals supplied to theswitch 135. The timing control unit 123 controls a timing point at whichthe converting unit 134 transmits the differential signal.

In addition, in order to perform full duplex IP communication using theCEC line 84 and the signal line 141 connected to the reserved pin andthe signal line for transmitting the SDA signal and the signal line fortransmitting the SCL signal, the HDMI (R) source 71 and the HDMI (R)sink 72 are configured, for example, as shown in FIG. 7. Note that thesame numbering will be used in describing FIG. 7 as was used indescribing FIG. 6, and the description thereof are not repeated whereappropriate.

The HDMI (R) source 71 includes a transmitter 81, a switching controlunit 121, and a switching control unit 171. In addition, the transmitter81 includes a converting unit 131, a switch 133, a switch 181, a switch182, and a decoding unit 183.

At a timing point when data is transmitted, the switch 181 is suppliedwith the SDA signal from the HDMI (R) source 71, while, at a timingpoint when data is received, the switch is supplied with the SDA signalfrom the receiver 82 or the constituent signal forming the differentialsignal corresponding to Rx data from the receiver 82. Under the controlof the switching control unit 171, the switch 181 selectively outputsone of the SDA signal from the HDMI (R) source 71, the SDA signal fromthe receiver 82, and the constituent signal forming the differentialsignal corresponding to Rx data.

That is, at a timing point when the HDMI (R) source 71 receives datatransmitted from the HDMI (R) sink 72, the switch 181 receives the SDAsignal transmitted from the receiver 82 via an SDA line 191 which is thesignal line for transmitting the SDA signal or the constituent signal ofthe differential signal corresponding to Rx data. The switch 161 thensupplies the received SDA signal or the constituent signal to the HDMI(R) source 71 or the decoding unit 183.

In addition, at a timing point when the HDMI (R) source 71 transmitsdata to the HDMI (R) sink 72, the switch 181 transmits the SDA signalsupplied from the HDMI (R) source 71 to the receiver 82 via the SDA line191. Alternatively, the switch 181 transmits no signals to the receiver82.

At a timing point when data is transmitted, the switch 182 is suppliedwith the SCL signal from the HDMI (R) source 71, while, at a timingpoint when data is received, the switch is supplied with the constituentsignal forming the differential signal corresponding to Rx data from thereceiver 82. Under the control of the switching control unit 171, theswitch 182 selectively outputs one of the SCL signal and the constituentsignal forming the differential signal corresponding to Rx data.

That is, at a timing point when the HDMI (R) source 71 receives datatransmitted from the HDMI (R) sink 72, the switch 182 receives theconstituent signal of the differential signal corresponding to Rx datatransmitted from the receiver 82 via an SCL line 192 which is a signalline for transmitting the SCL signal and supplies the receivedconstituent signal to the decoding unit 183. Alternatively, the switch182 receives no signals.

In addition, at a timing point when the HDMI (R) source 71 transmitsdata to the HDMI (R) sink 72, the switch 182 transmits the SCL signalsupplied from the HDMI (R) source 71 to the receiver 82 via the SCL line192. Alternatively, the switch 182 transmits no signals to the receiver82.

The decoding unit 183 includes, for example, a differential amplifier.Input terminals of the decoding unit 183 are connected to the SDA line191 and SCL line 192. The decoding unit 183 receives a differentialsignal transmitted from the receiver 82 via the SDA line 191 and SCLline 192, that is, the differential signal formed from the constituentsignal on the SDA line 191 and the constituent signal on the SCL line192. The decoding unit 183 then decodes the differential signal intooriginal Rx data and outputs the original Rx data.

The switching control unit 171 controls the switches 181 and 182 so thateach of the switches 181 and 182 is switched to select one of thesignals supplied thereto.

In addition, the HDMI (R) sink 72 includes a receiver 82, a switchingcontrol unit 124, and a switching control unit 172. Furthermore, thereceiver 82 includes a switch 135, a decoding unit 136, a convertingunit 184, a switch 185, and a switch 186.

The converting unit 184 is composed of, for example, a differentialamplifier. The converting unit 184 receives supplied Rx data. Theconverting unit 184 converts the supplied Rx data into a differentialsignal formed from two constituent signals. The converting unit 184 thentransmits the converted differential signal to the transmitter 81 viathe SDA line 191 and the SCL line 192. That is, the converting unit 184transmits one of the constituent signals forming the converteddifferential signal to the transmitter 81 via the switch 185. Theconverting unit 184 further transmits the other constituent signalforming the differential signal to the transmitter 81 via the switch186.

At a timing point when data is transmitted, the switch 185 is suppliedwith the constituent signal forming the differential signalcorresponding to Rx data from the converting unit 184 or the SDA signalfrom the HDMI (R) sink 72, while, at a timing point when data isreceived, the switch 185 is supplied with the SDA signal from thetransmitter 81. Under the control of the switching control unit 172, theswitch 185 selectively outputs one of the SDA signal from the HDMI (R)sink 72, the SDA signal from the transmitter 81, and the constituentsignal forming the differential signal corresponding to Rx data.

That is, at a timing point when the HDMI (R) sink 72 receives datatransmitted from the HDMI (R) source 71, the switch 185 receive the SDAsignal transmitted from the transmitter 81 via the SDA line 191. Theswitch 185 then supplies the received SDA signal to the HDMI (R) sink72. Alternatively, the switch 185 receives no signals.

In addition, at a timing point when the HDMI (R) sink 72 transmits datato the HDMI (R) source 71, the switch 185 transmits the SDA signalsupplied from the HDMI (R) sink 72 or the constituent signal suppliedfrom the converting unit 384 to the transmitter 81 via the SDA line 191.

At a timing point when data is transmitted, the switch 186 is suppliedwith the constituent signal forming the differential signalcorresponding to Rx data from the converting unit 184, while, at atiming point when data is received, the switch is supplied with the SCLsignal from the transmitter 81. Under the control of the switchingcontrol unit 172, the switch 186 selectively outputs one of the SCLsignal and the constituent signal forming the differential signalcorresponding to Rx data.

That is, at a timing point when the HDMI (R) sink 72 receives datatransmitted from the HDMI (R) source 71, the switch 186 receives the SCLsignal transmitted from the transmitter 81 via the SCL line 192. Theswitch 186 then supplies the received SCL signal to the HDMI (R) sink72. Alternatively, the switch 186 receives no signals.

In addition, at a timing point when the HDMI (R) sink 72 transmits datato the HDMI (R) source 71, the switch 186 transmits the constituentsignal supplied from the converting unit 184 to the transmitter 81 viathe SCL line 192. Alternatively, the switch 186 transmits no signals.

The switching control unit 172 controls the switches 185 and 186 so thateach of the switches 185 and 186 is switched to select ones of thesignals supplied thereto.

Furthermore, when the HDMI (R) source 71 and HDMI (R) sink 72 perform IPcommunication, whether half duplex communication or full duplexcommunication is available is determined by each of the configurationsof the HDMI (R) source 71 and HDMI (R) sink 72. Therefore, by referringto E-EDID received from the HDMI (R) sink 72, the HDMI (R) source 71determines whether it performs half duplex communication, full duplexcommunication, or bidirectional communication through exchange of theCEC signal.

For example, as shown in FIG. 8, E-EDID received by the HDMI (R) source71 includes a base block and an expansion block.

Data defined by “E-EDID1.3 Basic Structure” of the E-EDID1.3 standard isplaced at the head of the base block of E-EDID, followed by timinginformation identified by “Preferred timing” for maintainingcompatibility with existing EDID and timing information identified by“2nd timing” different from “Preferred timing” for maintainingcompatibility with existing EDID.

In the base block, “2nd timing” is followed by information indicating adisplay device name identified by “Monitor NAME” and informationidentified by “Monitor Range Limits” indicating the numbers ofdisplayable pixels when the aspect ratios are 4:3 and 16:9.

At the head of the expansion block, information on right and leftspeakers represented by “Speaker Allocation” is placed, followed by:data identified by “VIDEO SHORT” describing information on a displayableimage size, a frame rate, interlace or progressive, and data describingan aspect ratio; data identified by “AUDIO SHORT” describing informationon a playable audio codec method, a sampling frequency, a cut-offfrequency range, the number of codec bits and the like; and informationidentified by “Speaker Allocation” on right and left speakers.

In addition, “Speaker allocation” is followed by data identified by“Vender Specific” and defined by each vendor, timing informationidentified by “3rd timing” for maintaining compatibility with existingEDID, and timing information identified by “4th timing” for maintainingcompatibility with existing EDID.

Data identified by “Vender Specific” has a data structure shown in FIG.9. That is, the data identified by “Vender Specific” includes 0th to Nthone-byte blocks.

In the 0-th block located at the head of the data identified by “VenderSpecific”, the following information is placed: information identifiedby “Vendor-Specific tag code(=3) serving as a header that indicates thedata area of the data “Vender Specific” and information identified by“Length(=N) representative of the length of the data “Vender Specific”.

Information identified by “24 bit IEEE RegistrationIdentifier(0x000C03)LSB first” indicating the number “0x000C03”registered for HDMI (R) is placed in the 1st to 3rd blocks. Informationrepresentative of the 24-bit physical address (indicated by “A”, “B”,“C” and “D”) of a sink device is placed in the 4th and 5th blocks.

In addition, the following information is placed in the 6th block: aflag identified by “Supports-AI” indicating a function that the sinkdevice supports; information identified by “DC-48 bit”, “DC-36 bit” and“DC-30 bit” each indicating the number of bits per pixel; a flagidentified by “DC-Y444” indicating whether the sink device supportstransmission of an image of YCbCr 4:4:4; and a flag identified by“DVI-Dual” indicating whether the sink device supports a dual digitalvisual interface (DVI).

Furthermore, information identified by “Max-TMDS-Clock” representativeof the highest frequency of a TMDS pixel clock is placed in the 7thblock. Still furthermore, the following flags are placed in the 8thblock: a flag identified by “Latency” indicating presence/absence ofdelay information regarding video and sound, a full duplex flagidentified by “Full Duplex” indicating whether full duplex communicationis available, and a half duplex flag identified by “Half Duplex”indicating whether half duplex communication is available.

Here, for example, the full duplex flag that is set (e.g., set to “1”)indicates that the HDMI (R) sink 72 has a capability of conducting fullduplex communication, that is, the HDMI (R) sink 72 has theconfiguration shown in FIG. 7, whereas the full duplex flag that isreset (e.g., set to “0”) indicates that the HDMI (R) sink 72 does nothave a capability of conducting full duplex communication.

The half duplex flag that is set (e.g., set to “1”) indicates that theHDMI (R) sink 72 has a capability of conducting half duplexcommunication, i.e., the HDMI (R) sink 72 has the configuration shown inFIG. 6, whereas the half duplex flag that is reset (e.g., set to “0”)indicates that the HDMI (R) sink 72 does not have a capability ofconducting half duplex communication.

Delay time data of a progressive image identified by “Video Latency” isplaced in the 9th block of the data identified by “Vender Specific”.Delay time data, identified by “Audio Latency”, of audio signalsassociated with the progressive image is placed in the 10th block.Furthermore, delay time data, identified by “Interlaced Video Latency”,of an interlace image is placed in the 11th block. Delay time data,identified by “Interlaced Audio Latency”, of audio signals associatedwith the interlace image is placed in the 12th block.

In accordance with the full duplex flag and the half duplex flagcontained in E-EDID received from the HDMI (R) sink 72, the HDMI (R)source 71 determines whether it performs the half duplex communication,full duplex communication, or bidirectional communication throughexchange of the CEC signal. The HDMI (R) source 71 then performsbidirectional communication with the HDMI (R) sink 72 in accordance withthe determination result.

For example, if the HDMI (R) source 71 has the configuration shown inFIG. 6, the HDMI (R) source 71 can perform half duplex communicationwith the HDMI (R) sink 72 shown in FIG. 6. However, the HDMI (R) source71 cannot perform half duplex communication with the HDMI (R) sink 72shown in FIG. 7.

Therefore, when the electronic apparatus including the HDMI (R) source71 is powered on, the HDMI (R) source 71 starts a communication processand performs bidirectional communication corresponding to the capabilityof the HDMI (R) sink 72 connected to the HDMI (R) source 71.

The communication process performed by the HDMI (R) source 71 shown inFIG. 6 is described below with reference to the flowchart shown in FIG.10.

In step S11, the HDMI (R) source 71 determines whether a new electronicapparatus is connected to the HDMI (R) source 71. For example, the HDMI(R) source 71 determines whether a new electronic apparatus includingthe HDMI (R) sink 72 is connected thereto on the basis of the level of avoltage applied to a pin called “Hot Plug Detect” to which the signalline 86 is connected.

If, in step S11, it is determined that a new electronic apparatus is notconnected, communication is not performed. Accordingly, thecommunication process is completed.

However, if, in step S11, it is determined that a new electronicapparatus is connected, the switching control unit 121, in step S12,controls the switch 133 so that the switch 133 is switched to select theCEC signal from the HDMI (R) source 71 and select the CEC signal fromthe receiver 82 when data is received.

In step S13, the HDMI (R) source 71 receives E-EDID transmitted from theHDMI (R) sink 72 via the DDC 83. That is, upon detecting connection ofthe HDMI (R) source 71, the HDMI (R) sink 72 reads E-EDID from theEDIDROM 85 and transmits the read E-EDID to the HDMI (R) source 71 viathe DDC 83. Accordingly, the HDMI (R) source 71 receives the E EDIDtransmitted from the HDMI (R) sink 72.

In step S14, the HDMI (R) source 71 determines whether it can performhalf duplex communication with the HDMI (R) sink 72. That is, the HDMI(R) source 71 refers to the E-EDID received from the HDMI (R) sink 72and determines whether the half duplex flag “Half Duplex” shown in FIG.9 is set. For example, if the half duplex flag is set, the HDMI (R)source 71 determines that it can perform bidirectional IP communicationusing a half duplex communication method, i.e., half duplexcommunication.

If, in step S14, it is determined that half duplex communication isavailable, the HDMI (R) source 71, in step S15, transmits a signalindicating that IP communication based on a half duplex communicationmethod is performed using the CEC line 84 and the signal line 141, ascharnel information representative of a channel to be used for thebidirectional communication, to the receiver 82 via the switch 133 andCEC line 84.

That is, if the half duplex flag is set, the HDMI (R) source 71 can knowthat the HDMI (R) sink 72 has the configuration shown in FIG. 6 and thatit can perform half duplex communication using the CEC line 84 andsignal line 141. The HDMI (R) source 71 transmits the channelinformation to the HDMI (R) sink 72, so that the HDMI (R) sink 72 isinformed that half duplex communication is to be performed.

In step S16, the switching control unit 121 controls the switch 133 sothat the switch 133 is switched to select the differential signalcorresponding to Tx data from the converting unit 131 when data istransmitted and select the differential signal corresponding to Rx datafrom the receiver 82 when data is received.

In step S17, each component of the HDMI (R) source 71 performsbidirectional IP communication with the HDMI (R) sink 72 using the halfduplex communication method. Thereafter, the communication process iscompleted. That is, when data is transmitted, the converting unit 131converts the Tx data supplied from the HDMI (R) source 71 into adifferential signal and supplies one of constituent signals forming theconverted differential signal to the switch 133 and the otherconstituent signal to the receiver 82 via the signal line 141. Theswitch 133 transmits the constituent signal supplied from the convertingunit 131 to the receiver 82 via the CEC line 84. In this manner, thedifferential signal corresponding to the Tx data is transmitted from theHDMI (R) source 71 to the HDMI (R) sink 72.

When data is received, the decoding unit 132 receives a differentialsignal corresponding to the Rx data transmitted from the receiver 82.That is, the switch 133 receives the constituent signal of thedifferential signal corresponding to the Rx data transmitted from thereceiver 82 via the CEC line 84 and supplies the received constituentsignal to the decoding unit 132. Under the control of the timing controlunit 122, the decoding unit 132 decodes the differential signal formedfrom the constituent signal supplied from the switch 133 and theconstituent signal supplied from the receiver 82 via the signal line 141into the original Rx data. The decoding unit 132 then output theoriginal Rx data to the HDMI (R) source 71.

In this way, the HDMI (R) source 71 exchanges various data, such ascontrol data, pixel data, and audio data, with the HDMI (R) sink 72.

However, If, in step S14, it is determined that half duplexcommunication cannot be performed, each component of the HDMI (R) source71, in step S18, performs bidirectional communication with the HDMI (R)sink 72 by receiving and transmitting the CEC signal from and to theHDMI (R) sink 72. Thereafter, the communication process is completed.

That is, when data is transmitted, the HDMI (R) source 71 transmits theCEC signal to the receiver 82 via the switch 133 and CEC line 84. Whendata is received, the HDMI (R) source 71 receives the CEC signaltransmitted from the receiver 82 via the switch 133 and CEC line 84. Inthis way, the HDMI (R) source 71 exchanges the control data with theHDMI (R) sink 72.

In this manner, the HDMI (R) source 71 refers to the half duplex flagand performs half duplex communication with the HDMI (R) sink 72 capableof performing half duplex communication by using the CEC line 84 andsignal line 141.

As described above, by switching the switch 133 to select one oftransmission data and reception data and performing half duplexcommunication with the HDMI (R) sink 72 using the CEC line 84 and signalline 141, i.e., IP communication using a half duplex communicationmethod, high speed bidirectional communication can be performed whilemaintaining compatibility with existing HDMI (R).

In addition, like the HDMI (R) source 71, when the electronic apparatusincluding the HDMI (R) sink 72 is powered on, the HDMI (R) sink 72starts a communication process and performs bidirectional communicationwith the HDMI (R) source 71.

A communication process performed by the HDMI (R) sink 72 shown in FIG.6 is described below with reference to the flowchart of FIG. 11.

In step S41, the HDMI (R) sink 72 determines whether a new electronicapparatus is connected to the HDMI (R) sink 72. For example, the HDMI(R) sink 72 determines whether a new electronic apparatus including theHDMI (R) source 71 is connected on the basis of the level of a voltageapplied to the pin called “Hot Plug Detect” and to which the signal line86 is connected.

If, in step S41, it is determined that a new electronic apparatus is notconnected, communication is not performed. Thereafter, the communicationprocess is completed.

However, if, in step S41, it is determined that a new electronicapparatus is connected, the switching control unit 124, in step S42,controls the switch 135 so that the switch 135 is switched to select theCEC signal from the HDMI (R) sink 72 when data is transmitted and selectthe CEC signal from the transmitter 81 when data is received.

In step S43, the HDMI (R) sink 72 reads the E-EDID from the EDIDROM 85and transmits the readout E-EDID to the HDMI (R) source 71 via the DDC83.

In step S44 the HDMI (R) sink 72 determines whether channel informationtransmitted from the HDMI (R) source 71 is received.

That is, channel information indicating a bidirectional communicationchannel is transmitted from the HDMI (R) source 71 in accordance withthe capabilities of the HDMI (R) source 71 and the HDMI (R) sink 72. Forexample, if the HDMI (R) source 71 has the configuration shown in FIG.6, the HDMI (R) source 71 and HDMI (R) sink 72 can perform half duplexcommunication using the CEC line 84 and signal line 141. Therefore, thechannel information indicating that IP communication is performed usingthe CEC line 84 and the signal line 141 is transmitted from the HDMI (R)source 71 to the HDMI (R) sink 72. The HDMI (R) sink 72 receives thechannel information transmitted from the HDMI (R) source 71 via theswitch 135 and the CEC line 84 and determines that the channelinformation is received.

In contrast, if the HDMI (R) source 71 does not have the half duplexcommunication capability, the channel information is not transmittedfrom the HDMI (R) source 71 to the HDMI (R) sink 72. Accordingly, theHDMI (R) sink 72 determines that the channel information is notreceived.

If, in step S44, it is determined that the channel information isreceived, the processing proceeds to step S45, where the switchingcontrol unit 124 controls the switch 135 so that the switch 135 isswitched to select the differential signal corresponding to the Rx datafrom the converting unit 134 when data is transmitted and select thedifferential signal corresponding to the Tx data from the transmitter 81when data is received.

In step S46, each component of the HDMI (R) sink 72 performsbidirectional IP communication with the HDMI (R) source 71 using thehalf duplex communication method. Thereafter, the communication processis completed. That is, when data is transmitted, under the control ofthe timing control unit 123, the converting unit 134 converts the Rxdata supplied from the HDMI (R) sink 72 into a differential signal. Theconverting unit 134 then supplies one of constituent signals forming theconverted differential signal to the switch 135 and the otherconstituent signal to the transmitter 81 via the signal line 141. Theswitch 135 transmits the constituent signal supplied from the convertingunit 134 to the transmitter 81 via the CEC line 84. In this way, thedifferential signal corresponding to the Rx data is transmitted from theHDMI (R) sink 72 to the HDMI (R) source 71.

In addition, when data is received, the decoding unit 136 receives adifferential signal corresponding to the Tx data transmitted from thetransmitter 81. That is, the switch 135 receives the constituent signalof the differential signal corresponding to the Tx data transmitted fromthe transmitter 81 via the CEC line 84. The switch 135 then supplies thereceived constituent signal to the decoding unit 136. The decoding unit136 decodes the differential signal formed from the constituent signalsupplied from the switch 135 and the constituent signal supplied fromthe transmitter 81 via the signal line 141 into the original Tx data.The decoding unit 136 then outputs the original Tx data to the HDMI (R)sink 72.

In this manner, the HDMI (R) sink 72 exchanges various data, such ascontrol data, pixel data, and audio data, with the HDMI (R) source 71.

However, if, in step S44, it is determined that the channel informationis not received, each component of the HDMI (R) sink 72, in step S47,performs bidirectional communication with the HDMI (R) source 71 byreceiving and transmitting the CEC signal from and to the HDMI (R)source 71. Thereafter, the communication process is completed.

That is, when data is transmitted, the HDMI (R) sink 72 transmits theCEC signal to the transmitter 81 via the switch 135 and the CEC line 84.When data is received, the HDMI (R) sink 72 receives the CEC signaltransmitted from the transmitter 81 via the switch 135 and the CEC line84. In this way, the HDMI (R) sink 72 exchanges the control data withthe HDMI (R) source 71.

In this manner, upon receiving the channel information, the HDMI (R)sink 72 performs half duplex communication with the HDMI (R) sink 72 byusing the CEC line 84 and the signal line 141.

As described above, by switching the switch 135 so as to select one oftransmission data and reception data and performing half duplexcommunication with the HDMI (R) source 71 using the CEC line 84 and thesignal line 141, the HDMI (R) sink 72 can perform high-speedbidirectional communication while maintaining compatibility withexisting HDMI (R).

In addition, when the HDMI (R) source 71 has the configuration shown inFIG. 7 and the HDMI (R) source 71 performs a communication process, theHDMI (R) source 71 determines whether the HDMI (R) sink 72 has a fullduplex communication capability on the basis of the full duplex flagcontained in the E-EDID. The HDMI (R) source 71 then performsbidirectional communication in accordance with the determination result.

A communication process performed by the HDMI (R) source 71 shown inFIG. 7 is described below with reference to the flowchart shown in FIG.12.

In step S71, the HDMI (R) source 71 determines whether a new electronicapparatus is connected to the HDMI (R) source 71. If, in step S71, it isdetermined that a new electronic apparatus is not connected,communication is not performed. Therefore, the communication process iscompleted.

In contrast, if, in step S71, it is determined that a new electronicapparatus is connected, the switching control unit 171, in step S72,controls the switches 181 and 182 so that, when data is transmitted, theswitch 181 selects the SDA signal from the HDMI (R) source 71 and theswitch 182 selects the SCL signal from the HDMI (R) source 71 and, whendata is received, the switch 181 selects the SDA signal from thereceiver 82.

In step S73, the switching control unit 121 controls the switch 133 sothat the switch 133 is switched to select the CEC signal from the HDMI(R) source 71 when data is transmitted and select the CEC signal fromthe receiver 82 when data is received.

In step S74, the HDMI (R) source 71 receives the E-EDID transmitted fromthe HDMI (R) sink 72 via the SDA line 191 of the DDC 83. That is, upondetecting connection of the HDMI (R) source 71, the HDMI (R) sink 72reads the E-EDID from the EDIDROM 85 and transmits the readout E-EDID tothe HDMI (R) source 71 via the SDA line 191 of the DDC 83. Accordingly,the HDMI (R) source 71 receives the E-EDID transmitted from the HDMI (R)sink 72.

In step S75, the HDMI (R) source 71 determines whether it can performfull duplex communication with the HDMI (R) sink 72. That is, the HDMI(R) source 71 refers to the E-EDID received from the HDMI (R) sink 72and determines whether the full duplex flag “Full Duplex” shown in FIG.9 is set. For example, if the full duplex flag is set, the HDMI (R)source 71 determines that it can perform bidirectional IP communicationusing a full duplex communication method, that is, full duplexcommunication.

If, in step S75, it is determined that full duplex communication can beperformed, the switching control unit 171, in step S76, controls theswitches 181 and 182 so that the switches 181 and 182 are switched toselect the differential signal corresponding to the Rx data from thereceiver 82 when data is received.

That is, when data is received, the switching control unit 171 controlsswitching of the switches 181 and 182 so that, among the constituentsignals forming the differential signal corresponding to the Rx datatransmitted from the receiver 82, the constituent signal transmitted viathe SDA line 191 is selected by the switch 181, and the constituentsignal transmitted via the SCL line 192 is selected by the switch 182.

After the E-EDID is transmitted from the HDMI (R) sink 72 to the HDMI(R) source 71, the SDA line 191 and the SCL line 192 forming the DDC 83are not used, that is, transmission and reception of the SDA and SCLsignals via the SDA line 191 and the SCL line 192 are not performed.Therefore, by switching the switches 181 and 182, the SDA line 191 andthe SCL line 192 can be used as transmission lines of the Rx data forfull duplex communication.

In step S77, as channel information indicating a channel to be used forbidirectional communication, the HDMI (R) source 71 transmits, to thereceiver 82 via the switch 133 and the CEC line 84, a signal indicatingthat IP communication based on a full duplex communication method isperformed using a pair consisting of the CEC line 84 and the signal line141 and a pair consisting of the SDA line 191 and the SCL line 192.

That is, if the full duplex flag is set, the HDMI (R) source 71 can knowthat the HDMI (R) sink 72 has the configuration shown in FIG. 7 and thatfull duplex communication can be performed using a pair consisting ofthe CEC line 84 and the signal line 141 and a pair consisting of the SDAline 191 and the SCL line 192. Accordingly, the HDMI (R) source 71transmits the channel information to the HDMI (R) sink 72 in order toinform the HDMI (R) sink 72 that full duplex communication is performed.

In step S78, the switching control unit 121 controls the switch 133 sothat the switch 133 is switched to select the differential signalcorresponding to the Tx data from the converting unit 131 when data istransmitted. That is, the switching control unit 121 switches the switch133 so that the switch 133 selects the constituent signal of thedifferential signal supplied from the converting unit 131 andcorresponding to the Tx data.

In step S79, each component of the HDMI (R) source 71 performsbidirectional IP communication with the HDMI (R) sink 72 using the fullduplex communication method. Thereafter, the communication process iscompleted. That is, when data is transmitted, the converting unit 131converts the Tx data supplied from the HDMI (R) source 71 into adifferential signal. The converting unit 131 then supplies one ofconstituent signals forming the converted differential signal to theswitch 133 and the other constituent signal to the receiver 82 via thesignal line 141. The switch 133 transmits the constituent signalsupplied from the converting unit 131 to the receiver 82 via the CECline 84. In this manner, the differential signal corresponding to the Txdata is transmitted from the HDMI (R) source 71 to the HDMI (R) sink 72.

In addition, when data is received, the decoding unit 183 receives adifferential signal corresponding to the Rx data transmitted from thereceiver 82. That is, the switch 181 receives the constituent signal ofthe differential signal corresponding to the Rx data transmitted fromthe receiver 82 via the SDA line 191. The switch 181 then supplies thereceived constituent signal to the decoding unit 183. In addition, theswitch 182 receives the other constituent signal of the differentialsignal corresponding to the Rx data transmitted from the receiver 82 viathe SCL line 192. The switch 182 then supplies the received constituentsignal to the decoding unit 183. The decoding unit 183 decodes thedifferential signal formed from the constituent signals supplied fromthe switches 181 and 182 into the original Rx data and outputs theoriginal Rx data to the HDMI (R) source 71.

In this manner, the HDMI (R) source 71 exchanges various data, such ascontrol data, pixel data, and audio data, with the HDMI (P) sink 72.

However, if, in step S75, it is determined that full duplexcommunication cannot be performed, each component of the HDMI (R) source71, in step S80, performs bidirectional communication with the HDMI (R)sink 72 by receiving and transmitting the CEC signal from and to theHDMI (R) sink 72. Thereafter, the communication process is terminated.

That is, when data is transmitted, the HDMI (R) source 71 transmits theCEC signal to the receiver 82 via the switch 133 and CEC line 84 and,when data is received, the HDMI (R) source 71 receives the CEC signaltransmitted from the receiver 82 via the switch 133 and the CEC line 84.Thus, the HDMI (R) source 71 communicates the control data with the HDMI(R) sink 72.

In this manner, the HDMI (R) source 71 refers to the full duplex flagand performs full duplex communication with the HDMI (R) sink 72 capableof performing full duplex communication by using the pair consisting ofthe CEC line 84 and the signal line 141 and the pair consisting of theSDA line 191 and the SCL line 192.

As described above, by switching the switches 133, 181 and 182,selecting transmission data and reception data, and performing fullduplex communication with the HDMI (R) sink 72 by using the pairconsisting of the CEC line 84 and the signal line 141 and the pairconsisting of the SDA line 191 and the SCL line 192, high-speedbidirectional communication can be performed while maintainingcompatibility with existing HDMI (R).

As in the case of the HDMI (R) sink 72 shown in FIG. 6, when the HDMI(R) sink 72 has the configuration shown in FIG. 7, the HDMI (R) sink 72executes a communication process so as to perform bidirectionalcommunication with the HDMI (R) source 71.

A communication process performed by the HDMI (R) sink 72 shown in FIG.7 is described below with reference to the flowchart of FIG. 13.

In step S111, the HDMI (R) sink 72 determines whether a new electronicapparatus is connected to the HDMI (R) sink 72. If, in step S111, it isdetermined that a new electronic apparatus is not connected,communication is not performed. Therefore, the communication process iscompleted.

In contrast, if, in step S11, it is determined that a new electronicapparatus is connected, the switching control unit 172, in step S112,controls switching of the switches 185 and 186 so that, when data istransmitted, the switch 185 selects the SDA signal from the HDMI (R)sink 72 and, when data is received, the switch 185 selects the SDAsignal from the transmitter 81 and the switch 186 selects the SCL signalfrom the transmitter 81.

In step S113, the switching control unit 124 controls the switch 135 sothat the switch 135 is switched to select the CEC signal from the HDMI(R) sink 72 when data is transmitted and select the CEC signal from thetransmitter 81 when data is received.

In step S114, the HDMI (R) sink 72 reads the E-EDID from the EDIDROM 85and transmits the readout E-EDID to the HDMI (R) source 71 via theswitch 185 and the SDA line 191 of the DDC 83.

In step S115, the HDMI (R) sink 72 determines whether channelinformation transmitted from the HDMI (R) source 71 is received.

That is, channel information indicating a bidirectional communicationchannel is transmitted from the HDMI (R) source 71 in accordance withthe capabilities of the HDMI (R) source 71 and HDMI (R) sink 72. Forexample, when the HDMI (R) source 71 has the configuration shown in FIG.7, the HDMI (R) source 71 and HDMI (R) sink 72 can perform full duplexcommunication. Accordingly, the HDMI (R) source 71 transmits, to theHDMI (R) sink 72, channel information indicating that IP communicationby a full duplex communication method is performed using the pairconsisting of the CEC line 84 and the signal line 141 and the pairconsisting of the SDA line 191 and the SCL line 192. Consequently, theHDMI (R) sink 72 receives the channel information transmitted from theHDMI (R) source 71 via the switch 135 and the CEC line 84 and determinesthat the channel information is received.

However, if the HDMI (R) source 71 does not have the full duplexcommunication capability, the channel information is not transmittedfrom the HDMI (R) source 71 to the HDMI (R) sink 72. Accordingly, theHDMI (R) sink 72 determines that the channel information has not beenreceived.

If, in step S115, it is determined that the channel information has notbeen received, the processing proceeds to step S116, where the switchingcontrol unit 172 controls switching of the switches 185 and 186 so thatthe switches 185 and 186 select the differential signal corresponding tothe Rx data from the converting unit 184 when data is transmitted.

In step S117, the switching control unit 124 controls switching of theswitch 135 so that the switch 135 selects the differential signalcorresponding to the Tx data from the transmitter 81 when data isreceived.

In step S118, each component of the HDMI (R) sink 72 performsbidirectional IP communication with the HDMI (R) source 71 using a fullduplex communication method. Thereafter, the communication process iscompleted. That is, when data is transmitted, the converting unit. 184converts the Rx data supplied from the HDMI (R) sink 72 into adifferential signal and supplies one of constituent signals forming theconverted differential signal to the switch 185 and supplies the otherconstituent signal to the switch 186. The switches 185 and 186 transmitthe constituent signals supplied from the converting unit 184 to thetransmitter 81 via the SDA line 191 and the SCL line 192. In thismanner, the differential signal corresponding to the Rx data istransmitted from the HDMI (R) sink 72 to the HDMI (R) source 71.

In addition, when data is received, the decoding unit 136 receives thedifferential signal corresponding to the Tx data transmitted from thetransmitter 81. That is, the switch 135 receives the constituent signalof the differential signal corresponding to the Tx data transmitted fromthe transmitter 81 via the CEC line 84. The switch 135 then supplies thereceived constituent signal to the decoding unit 136. The decoding unit136 decodes the differential signal formed from the constituent signalsupplied from the switch 135 and the constituent signal supplied fromthe transmitter 81 via the signal line 141 into the original Tx data.The decoding unit 136 then outputs the original Tx data to the HDMI (R)sink 72.

In this manner, the HDMI (R) sink 72 exchanges various data, such ascontrol data, pixel data, and audio data, with the HDMI (R) source 71.

However, if, in step S115, it is determined that the channel informationhas not been received, each component of the HDMI (R) sink 72, in stepS119, performs bidirectional communication with the HDMI (R) source 71by receiving and transmitting the CEC signal from and to the HDMI (R)source 71. Thereafter, the communication process is completed.

In this manner, upon receiving the channel information, the HDMI (R)sink 72 performs full duplex communication with the HDMI (R) sink 72using the pair consisting of the CEC line 84 and the signal line 141 andthe pair consisting of the SDA line 191 and the SCL line 192.

As described above, by switching the switches 135, 185 and 186 so as toselect transmission data and reception data and performing full duplexcommunication with the HDMI (R) source 71 using the pair consisting ofthe CEC line 84 and the signal line 141 and the pair consisting of theSDA line 191 and the SCL line 192, the HDMI (R) sink 72 can performhigh-speed bidirectional communication while maintaining compatibilitywith existing HDMI (R).

While, in the configuration of the HDMI (R) source 71 shown in FIG. 7,the converting unit 131 is connected to the CEC line 84 and the signalline 141 and the decoding unit 183 is connected to the SDA line 191 andthe SCL line 192, the configuration may be used in which the decodingunit 183 is connected to the CEC line 84 and the signal line 141 and theconverting unit 131 is connected to the SDA line 191 and the SCL line192.

In such a case, the switches 181 and 182 are connected to the CEC line84 and the signal line 141, respectively. The switches 181 and 182 arefurther connected to the decoding unit 183. The switch 133 is connectedto the SDA line 191. The switch 133 is further connected to theconverting unit 131.

Similarly, in the configuration of the HDMI (R) sink 72 shown in FIG. 7,the converting unit 184 may be connected to the CEC line 84, and thesignal line 141 and the decoding unit 136 may be connected to the SDAline 191 and the SCL line 192. In this case, the switches 185 and 186are connected to the CEC line 84 and the signal line 141, respectively.The switches 185 and 186 are further connected to the converting unit184. The switch 135 is connected to the SDA line 191. The switch 135 isfurther connected to the decoding unit 136.

Furthermore, in FIG. 6, the CEC line 84 and the signal line 141 mayserve as the SDA line 191 and the SCL line 192. That is, the convertingunit 131 and the decoding unit 132 of the HDMI (R) source 71 and theconverting unit 134 and decoding unit 136 of the HDMI (R) sink 72 may beconnected to the SDA line 191 and the SCL line 192 so that the HDMI (R)source 71 and the HDMI (R) sink 72 perform IP communication using a halfduplex communication method. Still furthermore, in such a case,connection of an electronic apparatus may be detected by using areserved pin of the connector to which the signal line 141 is connected.

Furthermore, each of the HDMI (R) source 71 and the HDMI (R) sink 72 mayhave the half duplex communication capability and the full duplexcommunication capability. In such a case, the HDMI (R) source 71 and theHDMI (R) sink 72 can perform IP communication using a half duplexcommunication method or a full duplex communication method in accordancewith the capability of the connected electronic apparatus.

If each of the HDMI (R) source 71 and the HDMI (R) sink 72 has the halfduplex communication capability and the full duplex communicationcapability, the HDMI (R) source 71 and the HDMI (R) sink 72 areconfigured, for example, as shown in FIG. 14. Note that, in FIG. 14, thesame numbering is used in describing FIG. 14 as was used in describingFIG. 6 or 7, and the description thereof are not repeated whereappropriate.

An HDMI (R) source 71 shown in FIG. 14 includes a transmitter 81, aswitching control unit 121, a timing control unit 122, and a switchingcontrol unit 171. The transmitter 81 includes a converting unit 131, adecoding unit 132, a switch 133, a switch 181, a switch 182, and adecoding unit 183. That is, the HDMI (R) source 71 shown in FIG. 14 hasa configuration in which the timing control unit 122 and the decodingunit 132 shown in FIG. 6 are additionally provided to the HDMI (R)source 71 shown in FIG. 7.

In addition, an HDMI (R) sink 72 shown in FIG. 14 includes a receiver82, a timing control unit 123, a switching control unit 124, and aswitching control unit 172. The receiver 82 includes a converting unit134, a switch 135, a decoding 136, a converting unit 184, a switch 185,and a switch 186. That is, the HDMI (R) sink 72 shown in FIG. 14 has aconfiguration in which the timing control unit 123 and the convertingunit 134 shown in FIG. 6 are additionally provided to the HDMI (R) sink72 shown in FIG. 7.

A communication process performed by the HDMI (R) source 71 and the HDMI(R) sink 72 shown in FIG. 14 is described next.

First, a communication process performed by the HDMI (R) source 71 shownin FIG. 14 is described with reference to the flowchart shown in FIG.15. Since the processes performed in steps S151 to S154 are the same asthose performed in steps S71 to S74 shown in FIG. 12, respectively, andtherefore, the descriptions thereof are not repeated.

In step S155, the HDMI (R) source 71 determines whether it can performfull duplex communication with the HDMI (R) sink 72. That is, the HDMI(R) source 71 refers to E-EDID received from the HDMI (R) sink 72 anddetermines whether the full duplex flag “Full Duplex” shown in FIG. 9 isset.

If, in step S155, it is determined that full duplex communication isavailable, that is, if the HDMI (R) sink 72 shown in FIG. 14 or FIG. 7is connected to the HDMI (R) source 71, the switching control unit 171,in step S156, controls the switches 181 and 182 so that the switches 181and 182 are switched to select the differential signal corresponding toRx data from the receiver 82 when data is received.

However, if, in step S155, it is determined that full duplexcommunication is not available, the HDMI (R) source 71, in step S157,determines whether half duplex communication is available. That is, theHDMI (R) source 71 refers to the received E-EDID and determines whetherthe half duplex flag “Half Duplex” shown in FIG. 9 is set. In otherwords, the HDMI (R) source 71 determines whether the HDMI (R) sink 72shown in FIG. 6 is connected to the HDMI (R) source 71.

If, in step S157, it is determined that half duplex communication isavailable, or if, in step S156, the switches 181 and 182 are switched,the HDMI (R) source 71, in step S158, transmits channel information tothe receiver 82 via the switch 133 and the CEC line 84.

Here, if, in step S155, it is determined that full duplex communicationis available, the HDMI (R) sink 72 has a full duplex communicationcapability. Accordingly, the HDMI (R) source 71 transmits, to thereceiver 82 via the switch 133 and CEC line 84, a signal indicating thatIP communication is performed using a pair consisting of the CEC line 84and the signal line 141 and a pair consisting of the SDA line 191 andthe SCL line 192 as channel information.

However, if, in step S157, it is determined that half duplexcommunication is available, the HDMI (R) sink 72 has a half duplexcommunication capability although it does not have a full duplexcommunication capability. Accordingly, the HDMI (R) source 71 transmits,to the receiver 82 via the switch 133 and the CEC line 84, a signalindicating that IF communication is performed using the CEC line 84 andthe signal line 141, as channel information.

In step S159, the switching control unit 121 controls the switch 133 sothat the switch 133 is switched to select the differential signalcorresponding to the Tx data from the converting unit 131 when data istransmitted and to select the differential signal corresponding to theRx data transmitted from the receiver 82 when data is received. When theHDMI (R) source 71 and the HDMI (R) sink 72 perform full duplexcommunication, the differential signal, corresponding to the Rx data arenot transmitted from the receiver 82 via the CEC line 84 and the signalline 141 when the HDMI (R) source 71 receives data. Accordingly, thedifferential signal corresponding to the Rx data is not supplied to thedecoding unit 132.

In step S160, each component of the HDMI (R) source 71 performsbidirectional IP communication with the HDMI (R) sink 72. Thereafter,the communication process is completed.

That is, when the HDMI (R) source 71 performs full duplex communicationand half duplex communication with the HDMI (R) sink 72, the convertingunit 131 converts the Tx data supplied from the HDMI (R) source 71 intoa differential signal when data is transmitted. The converting unit 131then transmits one of constituent signals forming the converteddifferential signal to the receiver 82 via the switch 133 and the CECline 84 and transmits the other constituent signal to the receiver 82via the signal line 141.

When the HDMI (R) source 71 performs full duplex communication with theHDMI (R) sink 72 and when data is received, the decoding unit 183receives the differential signal corresponding to the Rx datatransmitted from the receiver 82 and decodes the received differentialsignal into the original Rx data. The decoding unit 183 then outputs theoriginal Rx data to the HDMI (R) source 71.

In contrast, when the HDMI (R) source 71 performs half duplexcommunication with the HDMI (R) sink 72 and when data is received, thedecoding unit 132 receives the differential signal corresponding to theRx data transmitted from the receiver 82 under the control of the timingcontrol unit 122. The decoding unit 132 then decodes the receiveddifferential signal into the original Rx data and outputs the originalRx data to the HDMI (R) source 71.

In this manner, the HDMI (R) source 71 exchanges various data, such ascontrol data, pixel data, and audio data, with the HDMI (R) sink 72.

However, if, in step S157, it is determined that half duplexcommunication is not available, each component of the HDMI (R) source71, in step S161, performs bidirectional communication with the HDMI (R)sink 72 by receiving and transmitting the CEC signal via the CEC line84. Thereafter, the communication process is completed.

In this manner, the HDMI (R) source 71 refers to the full duplex flagand the half duplex flag and performs full or half duplex communicationwith the HDMI (R) sink 72 in accordance with the capability of the HDMI(R) sink 72, which is a communication partner.

As described above, by switching the switches 133, 181 and 182 inaccordance with the capability of the HDMI (R) sink 72 serving as acommunication partner so as to select transmission data and receptiondata and performing full or half duplex communication with the HDMI (R)sink 72, high-speed bidirectional communication can be performed whilemaintaining compatibility with existing HDMI (R).

A communication process performed by the HDMI (R) sink 72 shown in FIG.14 is described next with reference to the flowchart shown in FIG. 16.Processes performed in steps S191 to S194 are the same as thoseperformed in steps S111 to S114 shown in FIG. 13, respectively, andtherefore, the descriptions thereof are not repeated.

In step S195, the HDMI (R) sink 72 receives channel informationtransmitted from the HDMI (R) source 71 via the switch 135 and the CECline 84. If the HDMI (R) source 71 connected to the HDMI (R) sink 72 hasneither the full duplex communication capability nor the half duplexcommunication capability, the channel information is not transmittedfrom the HDMI (R) source 71 to the HDMI (R) sink 72. Accordingly, theHDMI (R) sink 72 does not receive the channel information.

In step S196, the HDMI (R) sink 72 determines whether full duplexcommunication is performed or not on the basis of the received channelinformation. For example, if the HDMI (R) sink receives the channelinformation indicating that IP communication is performed using the pairconsisting of the CEC line 84 and the signal line 141 and the pairconsisting of the SDA line 191 and the SCL line 192, the HDMI (R) sink72 determines that full duplex communication is performed.

If, in step S196, it is determined that full duplex communication isperformed, the switching control unit 172, in step S197, controls theswitches 185 and 186 so that the switches 185 and 186 are switched toselect the differential signal corresponding to Rx data from theconverting unit 184 when data is transmitted.

However, if, in step S196, it is determined that full duplexcommunication is not performed, the HDMI (R) sink 72, in step S198,determines whether half duplex communication is performed on the basisof the received channel information. For example, if the HDMI (R) sink72 receives the channel information indicating that IP communicationusing the CEC line 84 and the signal line 141 is performed, the HDMI (R)sink 72 determines that half duplex communication in performed.

If, in step S198, it is determined that half duplex communication isperformed or if, in step S197, the switches 185 and 186 are switched,the switching control unit 124, in step S199, controls the switch 135 sothat the switch 135 is switched to select the differential signalcorresponding to Rx data from the converting unit 134 when data istransmitted and select the differential signal corresponding to Tx datafrom the transmitter 81 when data is received.

Note that, if the HDMI (R) source 71 and the HDMI (R) sink 72 performfull duplex communication, the differential signal corresponding to Rxdata are not transmitted from the converting unit 134 to the transmitter81 when data is transmitted at the HDMI (R) sink 72. Therefore, thedifferential signal corresponding to Rx data are not supplied to theswitch 135.

In step S200, each component of the HDMI (R) sink 72 performsbidirectional IP communication with the HDMI (R) source 71. Thereafter,the communication process is completed.

That is, if the HDMI (R) sink 72 and the HDMI (R) source 71 perform fullduplex communication and when data is transmitted, the converting unit184 converts Rx data supplied from the HDMI (R) sink 72 into adifferential signal. The converting unit 184 then supplies one ofconstituent signals forming the converted differential signal to thetransmitter 81 via the switch 185 and the SDA line 191 and supplies theother constituent signal to the transmitter 81 via the switch 186 andthe SCL line 192.

In addition, if the HDMI (R) sink 72 and the HDMI (R) source 71 performhalf duplex communication and when data is transmitted, the convertingunit 134 converts the Rx data supplied from the HDMI (R) sink 72 into adifferential signal. The converting unit 134 then transmits one ofconstituent signals forming the converted differential signal to thetransmitter 81 via the switch 135 and the CEC line 84 and transmits theother constituent signal to the transmitter 81 via the signal line 141.

Furthermore, if the HDMI (R) sink 72 and the HDMI (R) source 71 performfull duplex communication and half duplex communication and when data istransmitted, the decoding unit 136 receives the differential signalcorresponding to Tx data transmitted from the transmitter 81. Thedecoding unit 136 then decodes the received differential signal into theoriginal Tx data and outputs the original Tx data to the HDMI (R) sink72.

However, if, in step S198, it is determined that half duplexcommunication is not performed, that is, if, for example, the channelinformation is not transmitted, each component of the HDMI (R) sink 72,in step S201, performs bidirectional communication with the HDMI (R)source 71 by receiving and transmitting the CEC signal from and to theHDMI (R) source 71. Thereafter, the communication process is completed.

In this manner, the HDMI (R) sink 72 performs full duplex communicationor half duplex communication in accordance with the received channelinformation, that is, in accordance with the capability of the HDMI (R)source 71, which is the communication partner.

As described above, by switching the switches 135, 185 and 186 so as toselect transmission data and reception data in accordance with thecapability of the communication partner HDMI (R) source 71 andperforming full duplex communication or half duplex communication, amore suitable communication method can be selected and high-speedbidirectional communication can be performed while maintainingcompatibility with existing HDMI (R).

In addition, by connecting the HDMI (R) source 71 to the HDMI (R) sink72 using the HDMI (R) cable 35 which contains the CEC line 84 and thesignal line 141 twisted together to form a shielded differential pairand connected to the ground line and the SDA line 191 and the SCL line192 twisted together to form a shielded differential pair and connectedto the ground line, high-speed bidirectional IP communication based on ahalf duplex communication method or a full duplex communication methodcan be performed while maintaining compatibility with an existing HDMI(R) cable.

As described above, any one of one or more data items is selected astransmission data. The selected data is transmitted to a communicationpartner via a predetermined signal line. Any one of one or more dataitems transmitted from the communication partner is selected asreception data, and the selected data is received. Accordingly,high-speed bidirectional IP communication can be performed between theHDMI (R) source 71 and the HDMI (R) sink 72 via the HDMI (R) cable 35while maintaining compatibility with HDMI (R), that is, while allowinghigh-speed unidirectional transmission of uncompressed pixel data of animage from the HDMI (R) source 71 to the HDMI (R) sink 72.

As a result, if a source device (e.g., an electronic apparatus, such asthe reproducing apparatus 33 shown in FIG. 2) incorporating the HDMI (R)source 71 has, for example, a HDMI (Digital Living Network Alliance)server function and a sink device (e.g., an electronic apparatus, suchas the digital television set 31 shown in FIG. 2) incorporating the HDMI(R) sink 72 includes a LAN communication interface, such as Ethernet(registered trademark), content can be transferred from the sourcedevice to the sink device via the HDMI (R) cable through bidirectionalIP communication using an electronic apparatus (e.g., the amplifier 32)connected directly or via an HDMI (R) cable. In addition, the contentfrom the source device can be transferred from the sink device toanother device (e.g., the digital television set 34 shown in FIG. 2)connected to the LAN communication interface of the sink device.

Furthermore, with the bidirectional IP communication between the HDMI(R) source 71 and the HDMI (R) sink 72, control commands and responsescan be exchanged at high speed between a source apparatus incorporatingthe HDMI (R) source 71 and a sink apparatus incorporating the HDMI (R)sink 72 interconnected by the HDMI (R) cable 35. Therefore, quickresponse control can be realized between the apparatuses.

As described below, the above-described series of processes may berealized by dedicated hardware or software. When the series of processesare realized by software, the program forming the software is installedin, for example, a microcomputer that controls the HDMI (R) source 71and the HDMI (R) sink 72.

FIG. 17 illustrates an example of the configuration of a computer havingthe program for executing the above-described series of processesinstalled therein, according to an embodiment.

The program can be prerecorded in a recording medium, such as anelectrically erasable programmable read-only memory (EEPROM) 305 or aROM 303, incorporated in the computer.

Alternatively, the program can be temporarily or perpetually stored(recorded) in a removable recording medium, such as a compact discread-only memory (CD-ROM), a magneto optical (MO) disc, a digitalversatile disc (DVD), a magnetic disk, or a semiconductor memory. Thisremovable recording medium can be provided in the form of so-calledpackage software.

Note that, in addition to being installed from the above-describedremovable recording medium into the computer, the program may bewirelessly transferred from a download site to the computer via anartificial satellite for digital satellite broadcasting or may betransferred wired to the computer via a network, such as a LAN or theInternet. Subsequently, the computer can receive the transferred programusing an input/output interface 306 and install the program in abuilt-in EEPROM 305.

The computer incorporates a central processing unit (CPU) 302. Theinput/output interface 306 is connected to the CPU 302 via a bus 301.The CPU 302 loads the program stored in a read-only memory (ROM) 303 oran EPROM 305 into a random access memory (RAM) 304. The CPU 302 thenexecutes the program. In this way, the CPU 302 executes the processes inaccordance with the above-described flowcharts or the processesperformed in the configurations shown in the above-described blockdiagrams.

In this specification, processing steps that describe the program forcausing a computer to execute various processes need not be executed inthe sequence described in the flowcharts, but may contain processes tobe executed in parallel or independently (e.g., parallel processing or aprocess by an object).

In addition, the program may be executed by one computer or executed bya plurality of computers in a distributed manner.

The present invention is applicable to a communication interfaceincluding a transmitter and a receiver, in which the transmitterunidirectionally transmits a differential signal corresponding to pixeldata of an uncompressed image of one screen to a receiver via aplurality of channels in an effective video period which is a periodfrom one vertical synchronization signal to the next verticalsynchronization signal excluding horizontal blanking intervals and avertical blanking interval, and the receiver receives the differentialsignal transmitted via the plurality of channels.

In the present embodiment, bidirectional IP communication is performedby controlling, as needed, a data selection timing, a differentialsignal reception timing, and a differential signal transmission timingbetween the HDMI (R) source 71 and the HDMI (R) sink 72. However, thebidirectional communication can be performed using a protocol other thanIP.

The embodiment of the present invention is not limited to theabove-described embodiment, but various modifications can be madewithout departing from the spirit and scope of the invention.

According to the embodiment described above, bidirectional communicationcan be performed. In particular, high-speed bidirectional communicationcan be performed in a communication interface capable of transmittingpixel data of an uncompressed image and audio data associated with thepixel data while maintaining compatibility.

Additionally, many audio/video apparatuses have a LAN communicationcapability in order to provide interactive TV programs, highly advancedremote control, an electronic program guide and the like for the users,although some techniques thereof are the same as the already describedtechniques.

As means for forming a network among audio/video apparatuses, thefollowing alternatives, for example, can be provided: installation of adedicated cable, such as CAT5, wireless communication, and power linecommunication.

However, a dedicated cable makes the connection among the apparatusescomplicated. Wireless communication and power line communication havedisadvantages in that a required complicated modulation circuit and atransceiver are costly.

Accordingly, the above-described embodiment describes the techniques ofadding a LAN communication capability without adding a new connectorelectrode to HDMI. HDMI is an interface for performing data transmissionof video and audio data, exchange of connected device information,authentication of the connected device information, and communication ofdevice control data by using a single cable. Therefore, HDMI has asignificant advantage if a LAN communication capability is added to theHDMI and, therefore, LAN communication can be performed without using adedicated cable and wireless communication or the like.

Note that, in the techniques described in the above-describedembodiment, the differential transmission lines used for LANcommunication are also used for exchange and authentication of connecteddevice information and communication of device control data. In HDMI, aparasitic capacitance and an impedance of the electrical characteristicsof a connected device are strictly restricted for the DDC that performsexchange and authentication of the connected device information and theCEC that performs communication of device control data.

More specifically, a DDC terminal parasitic capacitance of a device isrequired to be 50 pF or lower. The DDC terminal is required to begrounded to ground GND with an impedance of 200Ω or lower when LOW isoutput and to be pulled up to a power source with an impedance of about2 kΩ in a HIGH state.

In addition, transmission/reception terminals are required to beterminated at least at about 100Ω in a high frequency range in order tostabilize LAN communication that transmits a high-speed signal.

FIG. 19 illustrates the state in which a transmitter 404 and a receiver405 are constantly AC-coupled to DDC lines of an existing HDMI sourcedevice 401 and an existing HDMI sink device 402.

In order to satisfy the DDC parasitic capacitance restrictions, a LANtransmitter and receiver circuit added to the DDC lines need to have ACcoupling via a sufficiently small capacitance. Therefore, a LAN signalis significantly attenuated, and therefore, is distorted. Consequently,a transmission and reception circuit for correcting the distortion maybecome complicated and costly.

In addition, transition between the HIGH and LOW states during DDCcommunication may interfere with LAN communication. That is, the LAN maynot function during DDC communication.

Accordingly, a communication system according to a more preferableembodiment is described below. The communication system is characterizedin that, in an interface that basically performs data transmission ofvideo and audio data, exchange and authentication of connected deviceinformation, communication of device control data, and LAN communicationby using a single cable, the LAN communication is performed throughbidirectional communication via a pair of differential transmissionlines, and a connection state of the interface is notified using the DCbias potential of at least one of the transmission lines.

Unlike the above-described embodiment, in the technique described below,a selecting unit is not necessarily required.

FIG. 18 is a circuit diagram illustrating a first example of theconfiguration of a communication system in which a connection state ofthe interface is notified using the DC bias potential of at least one ofthe transmission lines.

FIG. 19 illustrates an example of a system provided with Ethernet(registered trademark).

As shown in FIG. 18, this communication system 400 includes a LANfunction expansion HDMI (hereinafter referred to as “EH”) source device401, an EH sink device 402, an EH cable 403 for connecting the EH sourcedevice to the EH sink device, an Ethernet (registered trademark)transmitter 404 and an Ethernet (registered trademark) receiver 405.

The EH source device 401 includes a LAN signal transmitter circuit 411,a terminating resistor 412, AC coupling capacitors 413 and 414, a LANsignal receiver circuit 415, a subtracting circuit. 416, a pull-upresistor 421, a resistor 422 and a capacitor 423 forming a lowpassfilter, a comparator 424, a pull-down resistor 431, a resistor 432 and acapacitor 433 forming a lowpass filter, and a comparator 434.

The EH sink device 402 includes a LAN signal transmitter circuit 441, aterminating resistor 442, AC coupling capacitors 443 and 444, a LANsignal receiver circuit 445, a subtracting circuit 446, a pull-downresistor 451, a resistor 452 and a capacitor 453 forming a lowpassfilter, a comparator 454, a choke coil 461, and resistors 462 and 463connected in series between a power source potential and a referencepotential.

The EH cable 403 contains differential transmission lines composed of areserved line 501 and an HPD Line 502. Thus, a source side terminal 511of the reserved line 501, a source side terminal 512 of the HPD Line502, a sink side terminal 521 of the reserved line 501, and a sink sideterminal 522 of the HPD line are formed. The reserved line 501 and HPDline 502 are twisted together so as to form a twisted wire differentialpair.

In the source device 401 of the communication system 400 having such aconfiguration, the terminals 511 and 512 are connected to theterminating resistor 412, the LAN signal transmitter circuit 411, andthe LAN signal receiver circuit 415 via the AC coupling capacitors 413and 414.

The subtracting circuit 416 receives a sum signal SG412 of atransmission signal voltage generated by an electrical current outputfrom the LAN signal transmitter circuit 411 using the terminatingresistor 412 and the transmission lines 501 and 502 as loads and areception signal voltage of a signal transmitted from the EH sink device402.

In the subtracting circuit 416, a signal SG413 obtained by subtractingthe transmission signal SG411 from the sum signal SG412 is a net signaltransmitted from the sink.

The sink device 402 has a similar circuit network. With these circuits,the source device 4011 and the sink device 402 perform bidirectional LANcommunication.

In addition to performing the above-described LAN communication, byusing a DC bias level, the HPD line 502 sends, to the source device 401,information indicating that the cable 403 is connected to the sinkdevice 402.

When the cable 403 is connected to the sink device 402, the resistors462 and 463 and the choke coil 461 in the sink device 402 apply a biasto the HPD line 502 via the terminal 522 so that the HPD Line 502 isbiased at about 4 V.

The source device 401 extracts a DC bias of the HPD line 502 using thelowpass filter composed of the resistor 432 and the capacitor 433.Thereafter, the source device 401 compares the DC bias with thereference potential Vref2 (e.g., 1.4 V) using the comparator 434.

If the cable 403 is not connected to the source device 402, a potentialof the terminal 512 is lower than the reference potential Vref2 due tothe pull-down resistor 431. However, if the cable 403 is connected tothe source device 402, the potential is higher than the referencepotential.

Therefore, an output signal SG415 of the comparator 434 being HIGHindicates that the cable 403 is connected to the sink device 402.

In contrast, the output signal SG415 of the comparator 434 being LOWindicates that the cable 403 is not connected to the sink device 402.

The first example of the configuration further has a function ofmutually recognizing, using the DC bias potential of the reserved line501, whether the devices connected to either end of the cable 403 are EHcompatible apparatuses or HDMI apparatuses that are not compatible withEH.

The EH source device 401 pulls up (+5 V) the reserved line 501 by usingthe pull-up resistor 421, whereas the EH sink device 402 pulls down thereserved line 501 by using the pull-down resistor 451.

These resistors 421 and 451 are not included in an apparatus that doesnot support EH.

Using the comparator 424, the EH source device 401 compares a DCpotential of the reserved line 501 that has passed through the lowpassfilter composed of the resistor 422 and the capacitor 423 with areference voltage Vref1.

When the sink device 402 is EH compatible and is pulled down, thepotential of the reserved line 501 is 2.5 V. However, when the sinkdevice 402 is not EH compatible and is open, the potential of thereserved line is 5 V. Therefore, if the reference potential Vref1 is setto 3.75 V, it can be determined whether the sink device is EH compatibleor EH incompatible.

Using the comparator 454, the sink device 402 compares the DC potentialof the reserved line 501 that has passed through the lowpass filtercomposed of the resistor 452 and the capacitor 453 with a referencevoltage Vref3.

If the source device 401 is EH compatible and has a pull-up function,the potential of the reserved line 501 is 2.5 V. However, if the sourcedevice 401 is not EH compatible, the potential of the reserved line 501is 0 V. Therefore, if the reference potential is set to 1.25 V, it canbe determined whether the source device is EH compatible or EHincompatible.

As described above, according to the first example of the configuration,in the interface which performs data transmission of video data andaudio data, exchange and authentication of connected device information,communication of device control data, and LAN communication by using thesingle cable 403, the LAN communication is performed throughbidirectional communication via a pair of differential transmissionlines, and the connection state of the interface is notified by usingthe DC bias potential of at least one of the transmission lines.Therefore, spatial separation can be performed without physically usingthe SCL line and the SDA line for the LAN communication.

As a result, this division allows a LAN communication circuit to beformed independently from the electrical specifications defined for theDDC. Thus, stable and reliable LAN communication can be realized at lowcost.

Note that, the pull-up resistor 421 shown in FIG. 18 may be provided inthe EH cable 403, not in the source device 401. In such a case, theterminals of the pull-up resistor 421 are connected to the reserved line501 and a line (a signal line) connected to the power source (the powersource potential) of the lines provided in the EH cable 403.

In addition, the pull-down resistor 451 and the resistor 463 shown inFIG. 18 may be provided in the EH cable 403, not the EH sink device 402.In such a case, the terminals of the pull-down resistor 451 areconnected to the reserved line 501 and a line (a ground line) connectedto ground (the reference potential) of the lines provided in the EHcable 403. Furthermore, the terminals of the resistor 463 are connectedto the HPD Line 502 and the line (the ground line) connected to ground(the reference potential) of the lines provided in the EH cable 403.

FIG. 20 is a circuit diagram illustrating a second example of theconfiguration of the communication system in which a connection state ofthe interface is notified using the DC bias potential of at least one ofthe transmission lines.

Like the first example of the structure, this communication system 600is basically characterized in that, in the interface that performs datatransmission of video data and audio data, exchange and authenticationof connected device information, communication of device control data,and LAN communication by using a single cable, the LAN communication isperformed through unidirectional communication via two pairs ofdifferential transmission lines, and a connection state of the interfaceis notified using the DC bias potential of at least one of thetransmission lines, and in that at least two transmission lines are usedfor communication of exchange and authentication of connected deviceinformation in a time multiplexed manner with LAN communication.

As shown in FIG. 20, this communication system 600 includes a LANfunction expansion HDMI (hereinafter referred to as “EH”) source device601, an EH sink device 602, and an EH cable 603 for connecting the EHsource device to the Eli sink device.

The EH source device 601 includes a LAN signal transmitter circuit 611,terminating resistors 612 and 613, AC coupling capacitors 614 to 617, aLAN signal receiver circuit 618, an inverter 620, a resistor 621, aresistor 622 and a capacitor 623 forming a lowpass filter, a comparator624, a pull-down resistor 631, a resistor 632 and a capacitor 633forming a lowpass filter, a comparator 634, a NOR gate 640, analogswitches 641 to 644, an inverter 635, analog switches 646 and 747, DDCtransceivers 651 and 652, and pull-up resistors 653 and 654.

The EH sink device 602 includes a LAN signal transmitter circuit 661,terminating resistors 662 and 663, AC coupling capacitors 664 to 667, aLAN signal receiver circuit 668, a pull-down resistor 671, a resistor672 and a capacitor 673 forming a lowpass filter, a comparator 674, achoke coil 681, resistors 682 and 683 connected in series between apower source potential and a reference potential, analog switches 691 to694, an inverter 695, analog switches 696 and 697, DDC transceivers 701and 702, and a pull-up resistor 703.

The EH cable 603 contains differential transmission lines composed of areserved line 801 and an SCL line 803 and differential transmissionlines composed of an SDA line 804 and an HPD line 802. Thus, source sideterminals 811 to 814 and sink side terminals 821 to 824 are formed.

The reserved line 801 and the SCL line 803 are twisted together so as toform a twisted wire differential pair, and the SDA line 804 and HPD line802 are twisted together so as to form a twisted wire differential pair.

In the sink device 601 of the communication system 600 having such aconfiguration, the terminals 811 and 813 are connected to thetransmitter circuit 611 for transmitting a LAN transmission signal SG611to the sink via the AC coupling capacitors 614 and 615 and the analogswitches 641 and 642 and to the terminating resistor 612.

The terminals 814 and 812 are connected, via the AC coupling capacitors616 and 617 and the analog switches 643 and 644, to the receiver circuit618 for receiving a LAN signal from the sink device 602 and to theterminating resistor 613.

In the sink device 602, the terminals 821 to 824 are connected, via theAC coupling capacitors 664, 665, 666 and 667 and the analog switches 691to 694, to the transmitter and receiver circuits 668 and 661 and theterminating resistors 662 and 663.

The analog switches 641 to 644 and the analog switches 691 to 694 aremade conductive when LAN communication is performed and are made openwhen DDC communication is performed.

The source device 601 connects the terminals 813 and 814 to the DDCtransceivers 651 and 652 and the pull-up resistors 653 and 654 via theanalog switches 646 and 647, respectively.

The sink device 602 connects the terminals 823 and 824 to the DDCtransceivers 701 and 702 and the pull-up resistor 703 via the analogswitches 696 and 697, respectively.

The analog switches 646, 647, 696 and 697 are made conductive when DDCcommunication is performed and are made open when DLAN communication isperformed.

The recognition mechanism of an EH compatible apparatus using thepotential of the reserved line 801 is basically the same as that of thefirst example of the configuration, except that the resistor 62 of thesource device 601 is driven by the inverter 620.

When an input to the inverter 620 is HIGH, the resistor 621 functions asa pull-down resistor providing a 0-V mode from the viewpoint of the sinkdevice 602, as in the case where an EH compatible apparatus isconnected.

As a result, a signal SG623 indicating an EH compatibilityidentification result of the sink device 602 becomes LOW so that theanalog switches 691 to 694 controlled by the signal SG623 are made open,whereas the analog switches 696 and 697 controlled by a signal obtainedby inverting the signal SG623 using the inverter 695 are madeconductive.

As a result, the sink device 602 enters a mode in which the SCL line 803and the SDA line 804 are disconnected from the LAN transceiver and areconnected to the DDC transceiver.

On the other hand, in the source device 601, an input to the inverter620 is also input to the NOR gate 640 so that the output SG614 of theNOR gate 640 becomes LOW.

The analog switches 641 to 6444 controlled by the output signal SG614 ofthe NOR gate 640 are made open, whereas the analog switches 646 and 647controlled by a signal obtained by inverting the signal SG614 using theinverter 645 are made conductive.

As a result, the source device 601 also enters a mode in which the SCLline 803 and the SDA line 804 are disconnected from the LAN transceiverand are connected to the DDC transceiver.

In contrast, when an input to the inverter 620 is LOW, each of thesource device 601 and the sink device 602 enters a mode in which the SCLline 803 and the SDA line 804 are disconnected from the DDC transceiverand are connected to the LAN transceiver.

The circuits 631 to 634 and the circuits 681 to 683 used for examiningconnection using the DC bias potential of the HPD line 802 have thefunctions the same as those of the first example of the configuration.

That is, in addition to performing the above-described LANcommunication, by using the DC bias level, the HPD Line 802 sends, tothe source device 601, information indicating that the cable 803 isconnected to the sink device 802.

When the cable 803 is connected to the sink device 602, the resistors682 and 683 and the choke coil 681 in the sink device 602 applies a biasto the HPD line 802 via the terminal 822 so that the HPD line 802 isbiased at about 4 V.

The source device 601 extracts the DC bias of the HPD line 802 using thelowpass filter composed of the resistor 632 and the capacitor 633 andcompares the DC bias with the reference potential Vref2 (e.g., 1.4 V)using the comparator 634.

If the cable 603 is not connected to the source device 602, thepotential of the terminal 812 is lower than the reference potentialVref2 due to the pull-down resistor 631. However, if the cable 603 isconnected to the source device 602, the potential is higher than thereference potential Vref2.

Therefore, an output signal SG613 of the comparator 634 being HIGHindicates that the cable 803 is connected to the sink device 602.

In contrast, the output signal SG613 of the comparator 634 being LOWindicates that the cable 603 is not connected to the sink device 602.

As described above, according to the second example of theconfiguration, in the interface that performs data transmission of videodata and audio data, exchange and authentication of connected deviceinformation, communication of device control data, and LAN communicationby using a single cable, the LAN communication is performed throughunidirectional communication via two pairs of differential transmissionlines, and a connection state of the interface is notified by the DCbias potential of at least one of the transmission lines. Furthermore,at least two transmission lines are used for communication of exchangeand authentication of connected device information in a time multiplexedmanner with LAN communication. Accordingly, time multiplexing in whichthe time during which the SCL line and the SDA line are connected to theLAN communication circuit is separated from the time during which theSCL line and the SDA line are connected to the DDC circuit is available.This division allows a LAN communication circuit to be formedindependently from the electrical specifications defined for the DDC,and therefore, stable and reliable LAN communication can be realized atlow cost.

Note that, the resistor 621 shown in FIG. 20 may be provided in the EHcable 603, not in the EH source device 601. In such a case, theterminals of the resistor 621 are connected to the reserved line 801 anda line (a signal line) connected to the power source (the power sourcepotential) of the lines provided in the EH cable 603.

In addition, the pull-down resistor 671 and the resistor 683 shown inFIG. 20 may be provided in the EH cable 603, not the EH sink device 602.In such a case, the terminals of the pull-down resistor 671 areconnected to the reserved line 801 and a line (a ground line) connectedto ground (the reference potential) of the lines provided in the EHcable 603. Furthermore, the terminals of the resistor 683 are connectedto the HPD Line 802 and the line (the ground line) connected to ground(the reference potential) of the lines provided in the EH cable 603.

As described above, in the embodiment related to FIGS. 2 to 17, ofnineteen HDMI poles, SDA and SCL are used as a first differential pair,and CEC and Reserved are used as a second pair so that full duplexcommunication in which unidirectional communication is performed in eachpair is realized.

However, in SDA and SCL, communication is performed at 1.5 KΩ pull-upfor H and at a low impedance for L. In addition, in CEC, communicationis performed at 27 KΩ pull-up for H and at a low impedance for L.

If these functions are maintained in order to maintaining compatibilitywith existing HDMI, sharing of a LAN function for high-speed datacommunication that requires impedance matching at terminating ends of atransmission line may be difficult.

Therefore, in the first example of the configuration, full duplexcommunication is realized by using pair bidirectional communicationusing a differential pair of Reserved and HPD without using the SDA, SCLand CEC lines.

Since HPD is a DC-level flag signal, injection of a LAN signal using ACcoupling and transmission of DC-level plug information can be performedat the same time. A new function is provided to Reserved so that bothparties can mutually recognize that the terminal has a LAN function byusing a DC level and a method similar to that for HPD.

In the second example of the configuration, two differential pairs areformed using HPD, SDA, SCL, and reserved. Unidirectional communicationis performed by each of the pairs so that two-pair full duplexcommunication is realized.

In HDMI, the transmitter serves as a master at all times, and timing ofburst DDC communication using SDA and SCL is controlled by thetransmitter.

In this example, the analog switches are operated so that, when thetransmitter performs DDC communication, the SDA and SCL lines areconnected to the DDC transceiver and, when a transmitter does notperform DDC communication, the lines are connected to the LANtransceiver.

These switch control signals are also transmitted to the receiver usinga DC level of the Reserved line. Similar switching operations areperformed on the receiver side.

By employing the above-described configurations, a first advantage canbe provided in that SCL, SDA and CEC communication is not subjected tointerference by noise of LAN communication, and therefore, stable DDCand CEC communication can be ensured at all times.

This is because, in the first example of the configuration, a LAN isphysically disconnected from these lines and, in the second example ofthe configuration, a LAN signal is disconnected from these lines usingswitches during the DDC communication.

A second advantage is provided in that stable communication having awide margin is realized by performing LAN communication using the lineshaving ideal termination ends.

This is because, in the first example of the configuration, a LAN signalis superposed upon Reserved and HPD lines that transmit only DC-levelsignals, and therefore, a terminating impedance having an ideal valuecan be maintained in a sufficiently wide frequency range necessary forLAN communication, and in the second example of the configuration, LANterminating circuits that are not allowed to be used for DDCcommunication are connected using the switches only during LANcommunication.

FIGS. 21A to 21E are diagrams illustrating the waveforms ofbidirectional communication in the communication system of the first andsecond examples of the configurations.

FIG. 21A illustrates the waveform of a signal transmitted from an EHsink device. FIG. 21B illustrates the waveform of a signal received bythe EH sink device. FIG. 21C illustrates the waveform of a signalpassing through the cable. FIG. 21D illustrates the waveform of a signalreceived by an EH source device. FIG. 21E illustrates the waveform of asignal transmitted from the EH source device.

As can be seen from FIG. 21, according to the examples of theconfiguration, excellent bidirectional communication can be realized.

The invention claimed is:
 1. A reproducing apparatus forunidirectionally transmitting, to a receiver using a first differentialsignal, pixel data of an uncompressed image of one screen during aneffective video period representing a period from one verticalsynchronization signal to the next vertical synchronization signalexcluding horizontal blanking intervals and a vertical blankinginterval, the reproducing apparatus comprising: a decoding unitconfigured to decode pixel data serving as playback content to generatethe pixel data of the uncompressed image; a signal transmitting unitconfigured to transmit, to the receiver, a second differential signalrepresenting transmission data different from the pixel data of theuncompressed image via differential transmission lines formed from apair consisting of a first signal line and a second signal line; asignal receiving unit connected to the signal transmitting unit, thesignal receiving unit receiving a third differential signal transmittedfrom the receiver via the first signal line and the second signal line;and a subtracting circuit configured to subtract the second differentialsignal from the signal received by the signal receiving unit.
 2. Thereproducing apparatus according to claim 1, wherein the second signalline is an HPD signal line.
 3. The reproducing apparatus according toclaim 1, wherein the first signal line is a Reserved signal line.
 4. Thereproducing apparatus according to claim 1, further comprising: a deviceconnection detecting unit configured to detect whether the receiver isconnected via the differential transmission lines using a DC biaspotential of the second signal line.
 5. The reproducing apparatusaccording to claim 1, further comprising: a comparator configured tocompare a DC bias potential of the first signal line with apredetermined reference voltage.
 6. The reproducing apparatus accordingto claim 1, further comprising: a resistor in a circuit that connectsthe signal transmitting unit to the signal receiving unit.
 7. Atransmission method for use in a reproducing apparatus, the reproducingapparatus unidirectionally transmitting, to a receiver using a firstdifferential signal, pixel data of an uncompressed image of one screenduring an effective video period representing a period from one verticalsynchronization signal to the next vertical synchronization signalexcluding horizontal blanking intervals and a vertical blankinginterval, the method comprising the steps of: decoding pixel dataserving as playback content to generate the pixel data of theuncompressed image, transmitting by a signal transmitting unit, to thereceiver, a second differential signal representing transmission datadifferent from the pixel data of the uncompressed image via differentialtransmission lines formed from a pair consisting of a first signal lineand a second signal line; receiving, by a signal receiving unitconnected to the signal transmitting unit, a third differential signaltransmitted from the receiver via the first signal line and the secondsignal line; and subtracting, by a subtracting circuit, the seconddifferential signal from the signal received by the signal receivingunit.